Grinding noise after regear

I recently regeared to 4.88's and I have a grinding noise/vibration when I let off the gas at freeway speed. If I put it in neutral the sound amplifies and I can also hear a slight hum when I’m on the gas at the same speeds. After a few hundred miles I took the rear diff back out to check the pattern and the coast side looked like this.

I added and subtracted pinion shims to try and fix the pattern but the best I could get looks very similar to the picture above, just a bit more centered on the tooth (from toe to heel) and the pattern looks more like a crescent.

I put the diff back in and still have the same noise.

Everything I’ve read about nitro gears has been fantastic and the setup seems to be right so I’m not sure if that noise is coming from the differential, my driveline being out of balance, or something else.

Has anyone experienced a similar problem or have an idea of what the issue could be?

 

That was the gear pattern from mine when I regeared. Something looks amiss with your pattern, but I can't say for sure whether that is the cause of your noise. I assume it wasn't there before the gear swap?

 

That looks textbook. And no the noise want there before the swap. Or if it was I didn’t notice. I did my lift a few weeks before the re gear though. And I know the driveline is spinning a lot faster after going down to 4.88’s so I pulled the rear driveline and checked the angle on the transfer case and diff flange and I’m within a degree of them being the same. It’s also and access cab so there’s no carrier bearing.

 

Did you replace the front needle bearing?

 

I have not replaced the needle bearing because I'm pulling my front diff in two weeks. For now I have the front driveline out.

 

UPDATE:
After reading different posts on the forum I saw something about feeling driveline vibrations in the pedal if you were barefoot. So on my way home I slipped my boot off and couldn't feel anything noticeable. Then I started changing gears to see if it was just 5th and I noticed if I was in neutral and lightly bumped the synchro in third it affected the noise. I changed the gear oil in my tranny about 6k ago with Lucas synthetic 90 weight . But I checked the oil when it was still warm, it doesn't smell burnt or look discolored but it was a bit full. While I was under my truck I also checked the U joints on my driveline. They're fine but there is play in the slip yoke. So now I'm not sure if it's my driveline or transmission.

 

Take it to a driveline shop ,and they should be able to pinpoint the problem.

 

Factory driveshaft? Miles?

 

Factory driveshaft with almost 76k

 

Does anyone know of a good shop to take it to in the Reno NV area?

 

It was definitely the driveline, got it fixed, all good now!