Is this while moving..or just sitting still in gear?

It does it both times. Its a whirring sound and sometimes does it when in park.

I own (2) 500 CF Moto Z forces and they both hum when engaged in gear and going slow. Reverse or forward but it is much louder in reverse. Do they all do this? Is this normal?

That's the worst design I've ever seen. So there is no shoulder for that inner pinion bearing and if that yoke retainer bolt is loose...or breaks the pinion can be pulled-in? Wow...and I see where the aluminum is coming from. Bet my bolt is loose...like so many other CFM bolts are. Think I would find the best bolt made for that and give it some extra torque...with thread-loc.

It had a 10.9 10mm fine thread which is what I replaced it with. I could not find a 12.9 hex head at the hardware store. They were Allen heads.

Extra images

Here are internal pictures and closer views of where your aluminum shavings might be coming from.

Wow thank you! I wasnt sure if 800s and 500s were the same.

This is not an easy task to get the Gearbox out. The Allen bolts that mount the gearbox were so tight that I eventually had to drill 2 of them out because I could not break them loose before them getting striped out.

This bolt that broke is the ONLY thing keeping this from happening. Its the ONLY thing that holds the pinion gear in place. A horrible design if you ask me. I cant be the only one with this problem. We dont even drive it hard.

A replacement gearbox is over $1000 with a 30 day warranty from CF Moto.

Question: The ring gear is steel and is bolted to the carrier..the part that the pinion teeth are sliding through to and hitting the bolt ends. Is the carrier also steel..or is it aluminum?

I ask because sense new mine has had this bad clunking when going one direction gear position to another and it has been filling the oil with aluminum shavings or flakes so much so that I change it every 100 miles or so. It has slowed a bit but I have watched it and noticed something odd on that coupler between the engine and gear case. I know that the engine is rubber mounted and that have to have something that can deal with that movement as the gear case is solid mounted...and that have U-joints on the front driveline so that have this thing on the rear. Mine has always seemed to have this extra movement and causing something odd to happen to the diff/gear case when this clunking happens...like uneven power application to the axles. Weird. Along with this under power is a whine so loud..one needs to wear a helmet or ear plugs to keep from going deaf. I'm wondering if this ...or something like this might also be my problem. Something is chewing up aluminum in mine and this is making more and more sense to me after seeing it.

The carrier is steel. The aluminum shavings are probably from your cast aluminum gearbox. I will try to take pictures tomorrow but the pinion gear gouged the inside of my gearbox and thats where my aluminum shavings came from.

How old is this machine? That is to say is it under warranty?
If not, are you thinking of repair or replacement?

Its only a 2021. Out of warranty. I checked on a new replacement and their warranty is 30 days from CF Moto. Ridiculous to buy a new one to have to deal with it again in a year. I am looking at repair right now. Ive gone this far.

Follow up. It appears the bolt that holds the splined shaft on broke. This caused the shaft to get pushed in the gearbox and damage the second gear.

You cane see how far the shaft comes out of the differential. I dont think that is normal.

This is a new one. So where is the oil leaking from on the case? An axle seal...a crack...post a pic.

In other sound-related cases it's been a CV joint, a u-joint on the front drive line or carrier bearing, a shifter alignment problem or loose diff or engine mounting bolts.

It was coming out the front where the driveshaft connects. There is quite a bit of play it seems. I hope to have the differential out in the next few days. I will also snap a pic when I get the chance. I will look at the other things you mentioned as well. Thank you.

I was driving and let off the gas and the UTV started making a loud thwaping sound. I thought the drive shaft had broke and was hitting the undercarriage it sounded just like that. I stopped to look and didnt see anything immediately. So I turned around to drive back home and the noise would happen only when I let off the gas and the unit would naturally decel. If I applied a steady pressure on the gas to keep a load it was fine (I would push the gas and brake at the same time to slow down to stop). When I got it home I noticed oil leaking out of the rear end. I assumed that was the problem.

I currently am taking the rear end out but I am not sure if that is the problem or result of another problem. Does this sound like what would happen if the rear end was bad? The rear differential turns fine.