Odd hum/whine from rear while accelerating

[4WDTRK]

The sound is most noticeable taking off from a stop up to about 40mph. It's subtle, but the pitch and frequency change with increased RPM/speed. If I'm just cruising or at freeway speed I don't really notice it. Sounds like it's coming from the rear end/driveline area. Trans seems to shift fine and I don't have any check engine lights. I tow a boat a lot with this truck and it started during the end of my last tow.

I'm thinking of having the tires checked/rebalanced first, then changing the rear diff fluid, if all else fails I'll need to take it to the shop for a diagnosis.

Any ideas? Thanks!

 

[Scottydoggs]

id check the level/change the rear diff fluid. taking the cover off will let you see if theres any metal laying at the bottom too.

 

[4WDTRK]

Yea it's been a while since I've serviced the rear diff. Wouldn't be a bad time to change the fluid anyway. Thanks!

 

[4WDTRK]

I'm also suspecting a rear wheel bearing.

 

[rockola1971]

I suspect an axle or rear diff support bearing. My old Sierra had the same problem as yours for 2yrs or so before one day I decided to take it into my BIL tranny shop and we put it on the lift and tore it apart. It was the drivers side axle bearing which was pitted. So we changed them all and even put new clutch pucks in the locking differential. Cjeck your Ujoints too.

 

[4WDTRK]

Great info! I've got it scheduled to go into the shop Monday. I'll post the results.

 

[4WDTRK]

Serviced the rear diff and didn't notice anything abnormal. Refilled with RP 75W-90. Still have the noise. I'm getting the tires rotated and balanced today just to rule that out.

 

[4WDTRK]

Shop diagnosed today and says it's definitely ring/pinion wear and needs to be replaced.

So good and bad here. I have 3.42 gears and have always wished I was geared lower, especially for towing. So I'm planning to repair and swap to 3.73 gears. The bad is the cost, $3800 - $4200, waiting for a to the penny quote. Oh well at least it's cheaper than a new truck - definitely don't need that payment!

Should I even consider 4.10 gears? I'm running 285/70/17's. I don't want this thing wound too tight. 3.73's might be the sweet spot. Thanks!