[SWVProffitt]

Will try to get a video in a bit to attach.

2015 z8 ex 550miles.

Yesterday my wife and I decided to go on an adventure.  Rode nearly 100 miles, mostly road minus 1 trail (roughly 4 miles).  The trail had some pretty gnarly ruts (around 4 sections all together), but I took my time to navigate without bashing up the suspension.  Mostly had to handle them in 4wd low and downhill.  I noticed after the first one that when the rear end would release the tension exiting the rut, there was a loud clacking sound.  As if something was loose in the suspension.  It was so loud that I was positive it was damaging something.  So aside from a mammoth mudhole (no way around it) I avoided everything I could a rode the 10 ish miles back home via highway. 

When I got home I jumped straight on here to check all common issues. 

So far I have checked suspension bolts and mounts, a-arms, I have checked the driveshaft/ujoints (very little slack), and rear diff mount along with prying on engine to check engine mount slack.   So far nothing seems to be bad enough to cause that fatal-sounding clack.   

I'm open to any info to help track this down.  We ride this thing directly to the trails and have usually an hour to go to get to Hatfield's and outlaws from home along with 30mins ride to get to the bluestone wv area also.  Just want to stay on top of things so we don't have a break down too far from home. 

[NMKawierider]

Common...or at least some of the things that make suspension-related noises are..kind of in order:
Loose lug nuts or loose spacer mounting nuts, a failing CV joint or axle, Broken gear case mount, Broke, shock or mount, egged a-arm-to-frame mounting tab, Broken a-arm mounting tab, Broken sway bar, failing rear gear case, broken weld on the frame somewhere. 

[SWVProffitt]

Common...or at least some of the things that make suspension-related noises are..kind of in order:
Loose lug nuts or loose spacer mounting nuts, a failing CV joint or axle, Broken gear case mount, Broke, shock or mount, egged a-arm-to-frame mounting tab, Broken a-arm mounting tab, Broken sway bar, failing rear gear case, broken weld on the frame somewhere.

Using your message as a checklist I notice the upper A-arm bolt on the side that was making noise was able to be turned a little.   Very little as the impact seemed to only get an extra thread or two out of it.  Alas, this combined with the upper shock mount being able to be turned a thread or two also may help. 

Testing in trail behind house now.  Will update. 

[NMKawierider]

Common...or at least some of the things that make suspension-related noises are..kind of in order:
Loose lug nuts or loose spacer mounting nuts, a failing CV joint or axle, Broken gear case mount, Broke, shock or mount, egged a-arm-to-frame mounting tab, Broken a-arm mounting tab, Broken sway bar, failing rear gear case, broken weld on the frame somewhere.

Using your message as a checklist I notice the upper A-arm bolt on the side that was making noise was able to be turned a little.   Very little as the impact seemed to only get an extra thread or two out of it.  Alas, this combined with the upper shock mount being able to be turned a thread or two also may help. 

Testing in trail behind house now.  Will update. 

Clearly, as has been the case with most CFM products, the torque specs have not been adhered to at the factory. We advise everyone to go through all suspension, steering and component-related mounts and check the torque specs. For all CFM's we also "suggest" adding a little extra..ie "5" on top of what the book says. That's either 5ftlbs or inlbs to all listed specs. If you have one that's been loose enough to egg a hole, like maybe that a-arm, it may take 10 to stop it from moving or de-egg the hole with a welder and go with a better grade bolt...which I had to do with one front a-arm.

[SWVProffitt]

Common...or at least some of the things that make suspension-related noises are..kind of in order:
Loose lug nuts or loose spacer mounting nuts, a failing CV joint or axle, Broken gear case mount, Broke, shock or mount, egged a-arm-to-frame mounting tab, Broken a-arm mounting tab, Broken sway bar, failing rear gear case, broken weld on the frame somewhere.

Using your message as a checklist I notice the upper A-arm bolt on the side that was making noise was able to be turned a little.   Very little as the impact seemed to only get an extra thread or two out of it.  Alas, this combined with the upper shock mount being able to be turned a thread or two also may help. 

Testing in trail behind house now.  Will update. 

Clearly, as has been the case with most CFM products, the torque specs have not been adhered to at the factory. We advise everyone to go through all suspension, steering and component-related mounts and check the torque specs. For all CFM's we also "suggest" adding a little extra..ie "5" on top of what the book says. That's either 5ftlbs or inlbs to all listed specs. If you have one that's been loose enough to egg a hole, like maybe that a-arm, it may take 10 to stop it from moving or de-egg the hole with a welder and go with a better grade bolt...which I had to do with one front a-arm.

You arent wrong.  I didn't hear the noise but only had a few branches to flex it on and drop it off.  Looks like loctite and grade 8 are in my future...in mass.

When this tsunami weather clears up and the main trail by my house isn't impossible again, I will update on the noise. 

What I crazy is that I checked the upper shock mount for spec the night I bought it.  But it was clearly a little more loose last night.  Small investment to take a trip to Lowe's/home Depot to get rid of these poor quality bolts and nuts.

Thank you for the help. 

[SWVProffitt]

So I made a 210 mile journey today to the Outlaws and then back over o another trail system.  Really didn't hold back today.  Put it through it's paces on some hard trails and I found out that the loud clacking is in fact a LOT of slack in the rear diff. When I control the throttle better, it's like it isnt there. 

For now, crisis diverted.  Now to keep an eye on the diff life. 

[NMKawierider]

That's interesting cause I have had this strange .."banging" sound the last few years that I just can't find. My brain ID's the sound as a of a broken frame piece somewhere but I have inspected every inch of it and all bolts...on everything.. everywhere are ..well..over tight. But..I do have one very loose rear gear case. In fact it's so sloppy I'm surprised something hasn't come apart already Not only is it loose between the ring and pinion but the carrier and axle splines are loose enough that I can't believe one hasn't shredded already. And come to think of it my sound happens most often when coming down rough rocky trails with the throttle off or almost off. Next time it starts doing it I'll try some different throttle options.

[SWVProffitt]

That's interesting cause I have had this strange .."banging" sound the last few years that I just can't find. My brain ID's the sound as a of a broken frame piece somewhere but I have inspected every inch of it and all bolts...on everything.. everywhere are ..well..over tight. But..I do have one very loose rear gear case. In fact it's so sloppy I'm surprised something hasn't come apart already Not only is it loose between the ring and pinion but the carrier and axle splines are loose enough that I can't believe one hasn't shredded already. And come to think of it my sound happens most often when coming down rough rocky trails with the throttle off or almost off. Next time it starts doing it I'll try some different throttle options.

May have solved the mystery! 

I had to completely change the way I drive (throttle wise) and haven't heard it as much since.  I had a habit of keeping the Accel/decel as neutral as possible at times and when I was in a position that I needed to do "stop and go" navigating I would be on and off throttle frequently.  I.e. large ruts/rocks/logs.   

I have now gotten to where I transition easily from decel-accel and vice versa when trail cruising and when navigating the rough things I just do what I can and what noise happens, just happens. It is happening way less now.  I'm positive, now, that it is just a very loose drivetrain. Mainly rear diff.

I put it up on the lift today to wack the tires forward and rearward in their H/L range slack.  It was pretty loud by just using my own force.   
Figuring in the momentum, weight, and power of the machine, it's definitely my diff. Some driveline slack isn't helping matters either. 

At the rate I'm tacking miles on, we will see if it becomes a larger issue any time soon. 
I definitely am not going to cut this machine any slack.  Gotta see what it's made of. Haha

[NMKawierider]

That's interesting cause I have had this strange .."banging" sound the last few years that I just can't find. My brain ID's the sound as a of a broken frame piece somewhere but I have inspected every inch of it and all bolts...on everything.. everywhere are ..well..over tight. But..I do have one very loose rear gear case. In fact it's so sloppy I'm surprised something hasn't come apart already Not only is it loose between the ring and pinion but the carrier and axle splines are loose enough that I can't believe one hasn't shredded already. And come to think of it my sound happens most often when coming down rough rocky trails with the throttle off or almost off. Next time it starts doing it I'll try some different throttle options.

May have solved the mystery! 

I had to completely change the way I drive (throttle wise) and haven't heard it as much since.  I had a habit of keeping the Accel/decel as neutral as possible at times and when I was in a position that I needed to do "stop and go" navigating I would be on and off throttle frequently.  I.e. large ruts/rocks/logs.   

I have now gotten to where I transition easily from decel-accel and vice versa when trail cruising and when navigating the rough things I just do what I can and what noise happens, just happens. It is happening way less now.  I'm positive, now, that it is just a very loose drivetrain. Mainly rear diff.

I put it up on the lift today to wack the tires forward and rearward in their H/L range slack.  It was pretty loud by just using my own force.   
Figuring in the momentum, weight, and power of the machine, it's definitely my diff. Some driveline slack isn't helping matters either. 

At the rate I'm tacking miles on, we will see if it becomes a larger issue any time soon. 
I definitely am not going to cut this machine any slack.  Gotta see what it's made of. Haha

I'll do some testing myself next time mine starts doing it.