Question for the Jeep experts

[wanderingaimles]

I have a 2007 GC as a daily driver and my Toad.
4.7, 4wd
It has developed a hum, it seems to be a harmonic issue almost.
It starts at about 32 mph, gets louder until about 35 and stops between 38 and 40.
It only does it while accelerating, if I put it in neutral and rev nothing.
New engine, all gearboxes were serviced at 95,000.
I am assuming CV axles, 115,000 miles.
Is there anything Jeep specific that I should look for instead?
Shade tree doable or are there specific tools needed?

[Killingsworth]

I have a Jeep Wrangler, so your GC is probably different, how ever U joints is what I would be looking at, over the years Ive had U joints squeak, squeal, click and a variety of other sounds. It would be a place to check. If any are discolored, as in showing some signs of rust,or are loose etc. The other suggestions seem logical, pinion bearing, might see if the seal is leaking.

[MetalGator]

dodge guy wrote:
From a 30 year Jeep tech, it sounds like you’ve got a rear pinion bearing starting to fail!

This was the first thing I thought of when he said a hum at different speeds. My truck started doing the same thing. It started around 45mph and went away about 55mph. One of the pinion bearings was wearing out. Got the bearings replaced and the noise went away.

[dodge_guy]

From a 30 year Jeep tech, it sounds like you’ve got a rear pinion bearing starting to fail! I’ve never seen a CV shaft make a humming noise let alone fail. Pinion bearing are a common failure in the 90’s and 2000’s Mopars.

In fact I just did an 08 Commander (same as a Grand Cherokee) a month ago. Ended up doing all the bearings (pinion and carrier) while I was in there.

[wanderingaimles]

I bought it used at 95k miles and immediately had a jeep dealer service the tranny, Transfer case and both Diff's including replacing a seal in the rear.

[larry_cad]

Have you had the transfer case serviced regularly? That and the front differential are regularly forgotten in a service visit. The front differential is particularly vulnerable to damage. Best bet would be to have front and rear, and transfer case serviced all at the same time. Be careful of what you use in the transfer case. Chrysler is picky. Also you should refer to yours as a "WK".
Jeep drivers will recognize that as a 2005 to 2010 Grand Cherokee.

[theoldwizard1]

rjstractor wrote:
I'm not a Jeep guy, but from my experience CV joints usually click or clunk when failing. If the boots are intact I wouldn't replace them. If any of the boots are cracked, they are doomed to fail. Does the hum occur in any gear, or just the gear used during normal driving at that speed?

Concur !

The sure sign of impending doom on a CV joint is clicking on low speed turns. Even then you can put a significant number of miles on them before they do fall.

[wanderingaimles]

Normal driving, you can even feel it through the gas pedal.
At 35 when its at its loudest drop to neutral and it stops, even if you rev the engine.
No shake, no shimmy, but it sounds almost like a french horn.

[rjstractor]

I'm not a Jeep guy, but from my experience CV joints usually click or clunk when failing. If the boots are intact I wouldn't replace them. If any of the boots are cracked, they are doomed to fail. Does the hum occur in any gear, or just the gear used during normal driving at that speed?