Noise from Duramax Truck

[Brunton]

Yesterday I drove two new 2006 chevy crew cab pick ups with the LLY duramax engines. They both had less than 100 miles on them. While driving them on the highway between 65 and 70 mph they both made a very deep humming noise (the best I can describe it). When I backed off to below 65 mph they got quiet again and when I sped up to above 70 they also both got quiet. I had several people ride with me and they heard it too. I put the allison in M and shifted to 5th gear where the rpm went from about 1700 to 2000 rpm and the noise disappeared so I suspected it was coming from the engine/transmission.

Is this normal or is there something going on with the vehicles.

[mark45678]

I am not 100% sure but the lly trucks are poss older 2006 trucks, i think any thing made after Oct 2005 got a LBZ. I recall last thanks giving looking at trucks and it was right around that time the LBZ motor started showing up on the dealer lots.

The turbo makes a whine at low load and the more boost it makes the less noise the human ear can detect , poss this is what your hearing? My LBZ makes a lugging noise that I can hear around 1400~1500 rpm , I think the drive shaft is mostly where the noise comes from but it could be soemthing else also. out of the 3 duramax trucks I have owned the the 2006 has the best engine/trans combo of any year (stock). I know the lb7 (2001 ~2003) has more HP with aftermarket mods but def not as smooth running. the lly 2004.5 was ok but the turbo bark really gets old after 80000 mile and no answers from GM. I know the edge box made it worse but in the end the injector harnes failing iced it.

[Stlheadake]

I got my 06 LLY in April right when everyone else was getting their LBZ motors. I got the deal I got because it was a left over LLY. Now, that said, I haven't heard that noise. And I am particularly atune to strange noises (I won't go into how long I have been married either...) becuase I get that all the time regarding our car.

Mine under a load or heavy accelleration makes a loud noise that sounds like the turbo is leaking. I wondered is that normal or is my turbo leaking? I hear it on the driver's side mostly, and only when I am pushing the truck with a load. I can hear the turbo spool, but I hear a loud noise sounds like it is right under the driver's door and it sounds like air escaping from somewhere (exhaust?) or something?

I am new to the turbo diesel thing, and I just want to be sure that I don't have another thing to worry about. Is that a noise that I should be concerned about, or is it just turbo power?

[More Power]

It might be a good idea to go over the intercooler (charge air cooler) hose clamps. Loose clamps would allow boost to leak at a loose joint, and cause a hissing noise.

Jim

[Stlheadake]

Thanks MorePower, you hit the nail on the head. Is this a normal sound? It is loud. I mean ANYONE around me it's ALL they hear. I'm going to go through and change all the oils underneath next weekend, I'll have a look at it for leaks or loose clamps.

Thanks,

[titanite]

I have a 2005 LLY and it does the same thing, right around 100km/hr (1800-1900 RPM), louder hum noise, goes away above and below this speed. Never had it explained.

[SoTxPollock]

For what its worth, I'd try and find someone to bring the engine up to that RPM while you stand outside and observe the exhaust system. It could be vibrating, may need some additional damping at the hangers.