Engine Shudder

[JoeZ]

On my 2002 2500 Avalanche when I restart it hot, there is a growling howling shudder vibration for about two seconds after it starts. It runs perfectly well, but when there is a passenger that hasn't heard the noise before they jump when they hear it. The dealer couldn't find out what is doing it, as the noise is gone so quickly it seems impossible to pinpoint. Has anybody else noitced anything like this? It is like a "BrrRoar".

 

[RJLACK]

Not to sure about this one - since it does it hot only maybe it is the fan clutch just after start up it has become heat soaked and is stiff therefore it will roar for a second before it slows down. I will do some research and get back to ya if I find anything.

 

[JoeZ]

It's not the fan. It almost sounds like it is in the exhaust system. I have had myself and others stand all around the vehicle when it starts, and we all seem to hear it coming from a different place. I have been been fixing these things for over 35 years, and this one has me stumped. Sometimes when I am pulling my trailer and stop for gas then restart it it is the worst. Everybody nearby turns and looks. It doesn't affect anything, just that it is so loud that you know that something isn't right. Otherwise it will pull my 11,000 lb trailer all day at 70 to 80 without a squalk or squeak.

 

[victory_red]

I had the exact same thing happen on a different vehicle a few yrs ago. Every time I would start it up,it would make a deep roaring sound.Seemed liked it was worse once the car was warmed up a bit. I lived with it for a few weeks then suddenly my starter went out.After replacing my starter..the noise was gone. It seemed the started wasn't disengaging the bendix fast enough and it was getting caught up in the flywheel causing the noise. It wasn't a grinding noise or anything so the starter was the last thing I thought it would have been but it was the culprut.

 

[lld_eman]

Had a similar sound. turned out to be the catalyst material inside the cats broken loose. Ran fine, but a mechanic verified my findings and said he sees it regularly. He said that at some point it would break more off and allow pieces to turn sideways in the Cat and would block the exaust path. Then I would have a "Really bad Day!" such as damages to heads and head gaskets from major instant head pressure.
I replaced the Cats, and sure enough the problem was gone. That was about 2 years ago, and now I am suspecting the same issue is returning slowly, because I hear a rattling that sounds very sililar to what I had heard before every now and then.