drone noise

[NJDMAX]

I have been hearing a drone type noise when the truck is cold.The temps. have been upper 30's to low 40's at night. It goes away after the truck warms up after about 5 minutes. Is this caused by the fuel being cold? I do use FPPF Total Power in every tank full.

[Vette Racer]

The zrone noise you hear, is it like a vibration in the dash or something off to the passenger side. My 2002 has a noise like that when cold but goes away when it warms up. If you take it off idle, it quits. Just kind of annoying. Was wondering if maybe we have the same noise?

[Idle_Chatter]

NJDMax, that "drone" could very well be the Allison tranny (you do have the Allison, right?). The Ally pump is a monster and will make more noise when cold and the fluid is thicker.

[Tim B]

I'll bet it's the fan clutch. Mine makes a racket for a few minutes in the morning when I start up. I seem to remember something about the silicone in there being thick and needs to warm up. After it does, it decouples and the noise goes away.

Tim B.

[NJDMAX]

Well I heard it again this morning,It's not the transmission or the fan. It's coming from the exhaust system(stock). I walked around the truck while it was happening and I put my foot on the muffler and it stopped. I'll keep everyone posted on what the cause is once it stops raining and I can get under the truck.
Thanks, Tom

[BigLakeDMAX]

I notice a very mechanical noise from my exhaust when the truck is cold. It's a rythmic knocking sound, very regular in timing, and is audible at the tailpipe only. It's like someone tapping on one end of a long pipe while you're listening at the other. The engine sounds very smooth and typical diesel up front. This sound goes away when the engine is warm. Is this what you're hearing? Or is anyone else hearing what I am? I suspect part of it is the Duramax is so much quieter than my 97 6.5 that I can hear many sounds that I likely couldn't with my old truck.

[SoCalDMAX]

NJDMAX,

A few guys reported broken downpipe hangers which might make a rattling noise. Take a look in the PS fenderwell where the PS exhaust manifold and downpipe pass each other. There's a hanger there that supports the downpipe, check for a crak in a weld or seam.

Good luck! Steve

[NJDMAX]

SoCalDMAX, Yes the suppport bracket is snapped.There is a gap about an 1/8" wide. I'll start with having that fixed. Thanks Tom

BiglakeDmax, You may be hearing the same noise I am,you can see if the support is cracked using a mirror and light,look at the welded bracket on the turbo outlet pipe. Hope this helps,Tom

Thanks everyone, Tom