2004 gmc 2500 HD issues.

[billybek]

Driving the truck loaded with camper and gear today. The truck started to make an interesting noise but only when coasting downhill allowing the motor and drivetrain to slow the rig down a bit. Travelling through the mountains and some of these downhills can be several miles in length.
After coasting for a while a noise that sounds like a Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz kind of thing. Fairly loud.
Turn off radio. Not that
Shift trans to N. Still noisy. Rev the engine to 2500 rpm while in N. sound goes away.
I remember that this happened once about 3 or 4 years ago and had never done it again until today. Only 96000 km on truck. 6 litre gas 4x4
Any ideas?

[unclebilly]

Idler pulley or alternator. That’s my guess.

[rfuerst911sc]

Could be transfer case chain rattle , this era GM truck are known to have the transfer case oil pump ( aluminum ) chew a small hole in the case ( magnesium ) . Once that happens the ATF fluid will leak out of the transfer case . Crawl under the truck and look at the transfer case on the back side , the side facing the rear axle . Mine was at aprox. the 1:00 o'clock position . When enough fluid has leaked out ( only holds 2 quarts ) the chain starts to get noisy .

If it turns out to be the leaking transfer case issue my short term fix was the JB Weld trick , You Tube has plenty of videos . My long term solution was to replace the rear case half with an aftermarket aluminum case .

[billybek]

No evidence of leaking transfer case and low mileage 60000 miles on the truck. Sounds like that happens when more miles are on them.
Only happens when coasting with engine slowing the truck on long downhills

[fastfredracing]

My buddies had his torque convertor replaced under warranty with fairly low miles due to some odd noises. I think there may have been a TSB on it .
Ill see if I can find it for you.
His was a 2005 2500 HD 6.0 Gas, I have the same truck as you 220.000 miles, ans still runs great

[billybek]

Great thanks!
I will be fixing this one for a while.
Still runs well and does what I need t to do.
Looks good too!
Noticed last night that I have a rear axel seal leaking on the right side. Noticed a stripe around the wheel well.

[Sooner or later]

Originally Posted by fastfredracing

My buddies had his torque convertor replaced under warranty with fairly low miles due to some odd noises. I think there may have been a TSB on it .
Ill see if I can find it for you.
His was a 2005 2500 HD 6.0 Gas, I have the same truck as you 220.000 miles, ans still runs great

You are correct. Had one replaced free of charge in a Savana van.

[Brian 162]

I had a similar issue but it was intermittent. Turned out to be a front hub bearing. Vehicle was a Tahoe.

[SeanPizzle]

I have a 2500 2005 Yukon XL 4WD. Maybe the way the drivetrain was getting torqued in downhill engine braking caused the engine to shift against worn engine mounts and allow the fan to rub on the fan shroud. Look at the shroud for rub marks.

[billybek]

I will look for that. Thanks.

[billybek]

No marks on the fan shroud.