mY '02 hd 8.1 makes a noise similiar to a power steering pump low on fluid, but this is not the case. From what I have heard, it is actually the front pump of the allison trans. experiencing a slight cavitation and the noise is heard toward the front of the engine because of the drain back of trans. fluid in the lines. GM apparently resolved the issue with a check valve on the '03 models.
CAN ANY ONE SHINE MORE LIGHT ON THIS AND WHERE DOES THAT CHECK VALVE GO? i WOULD LIKE TO GET RID OF THE NOISE, GM SAYS IT'S OK, BUT SURE SOUNDS BAD.

tHANKS,
sTEVE

 

My 03 HD with the 6.0 & 4l80e makes the same noise and I've also been told this is normal. Between that and the cold start piston slap I nearly go insane at times. Sorry I can't help, but you aren't the only one with the problem. If you find the solution, post it up.