thup, thup, thup noise in driveline

[sdeck]

Hi All,

2002 Yukon XL 5.3L 4X4 1500. I've searched through this forum and haven't really found this noise described. It has been very hard to pinpoint where its coming from. While in the truck, it sounds like mid- to rear. If I'm hanging out the rear hatch while my 15 year old daughter is driving, it seems to be in the rear of the truck, but could be further up. I can't pinpoint left or right side so I'm going with the middle. Sounds like a thup-thup-thup-thup… almost like a muted playing card on a bicycle wheel sound or a piece of loose plastic flapping in the breeze. It is very rhythmic, not intermittent, but the pitch and volume changes a bit with engine load. Sound is the same in 2WD or 4WD. The frequency is faster than wheel rotation so its not a bolt stuck in the tread or anything. It occurs most noticeably at low speed (10 mph or less). Its not a grinding sound like brakes dragging or e-brake cable rubbing or anything. Gets to a steady light growl/hum at faster speeds. Occurs while moving in neutral and when coasting with engine off. No noise when stopped, engine running. I can't reproduce it on the jack stands, even with engine running and rear wheels turning. Turning driveshaft by hand does give me some squeaking from front drive shaft transfer case end u-joint (I think). The u-joints themselves seem tight by hand, but they are original (235,000 miles).

I have changed the transfer case fluid (no change in noise) and changed the rear axle bearings/rear diff fluid (no change in noise). Inside of rear diff looked fine. no metal pieces or chunks, just 235,000 miles worth of filings on the magnet. Rear pads and inner shoes look good so I don't think its brake parts dragging. I just changed the valve body a month ago to fix the torque converter intermittent lock up issue.

I'm planning on doing the u-joints this weekend. I need to get this figured out or my wife is going to run out and buy a Touareg…..

 

[OR VietVet]

My guess is the noise goes away with the old u-joints. I was going to say the tires could have a weird wear pattern but you can rotate and see if noise changes. My vote is the u-joints, especially with the miles on them.

 

[Sasquatch]

I think you`re right in starting with the u joints. I`m really surprised that the originals lasted almost a quarter million miles.

If it still makes the noise after that try to get a video of the noise and hopefully someone will recognize it.

 

[NCTyphoonKid]

That's a lot of miles for original u - joints. More than likely it is the u-joints.

 

[sdeck]

Changed all 4 u joints and front diff fluid. Noise is still there.

Diff drain had some metal filings on it but not unreasonable. Fluid came out looking mostly normal but top/last layer was light goldish. Looked like lots of tiny bubbles. I'm letting it sit a few days. Seemed like the right volume came out but i did notice wetness around passenger side axle shaft seal.

I can't localize this noise. It's a little more distinct that the title suggests but it definitely not a grinding or squealing. Doesn't really sound like a wheel bearing, no change in sound when turning either direction but ??? I'm starting to think it must be internal in the TC or one of the diffs. Is there any way to localize this?

Lastly, if I'm coasting in drive at 5-10 mph, it gets louder and more distinct if I put it in neutral. If I'm hearing it in neutral and give it a bit of gas, the noise changes tone a little.

Any ideas?

 

[SLCHOE]

Are the driveshafts noticeably bent? May be out of balance shafts. Don't know if you have acess but I'd put it up on a lift in 4wd with someone running it up to 50 mph and look at those drive shafts.

If you don't have access, try crawling underneath and with both hands shaking the driveshafts near the transfercase and at both axles looking for bad bearings.

 

[sdeck]

Shafts look pretty good. No movement at any end.

 

[Sasquatch]

The fact that it the noise changes when you rev the engine has me confused as to what it could be. If it was in the differentials or T-case i can`t see how engine rpm would affect it.

I was thinking it could be a cracked flexplate But that makes a different noise than you describe.

 

[sdeck]

you and me both. Here's audio of the sound. This is from front passenger seat, with the engine off, coasting in neutral, maybe 10ish mph.

http://vid107.photobucket.com/albums/m304/stevedeck/02 yukon driveline noise.mp4

 

[SLCHOE]

Occurs while moving in neutral and when coasting with engine off. No noise when stopped, engine running.

Definitely driveline related. Maybe unbalanced shafts, worn T-Case or diff pinion bearings, etc. All those spin in neutral with engine off.