Howling/Vibration noise at certain RPMs.

McCrae · March 25, 2015

Hey all, I'm new to posting on these forums, though I've lurked here every once and awhile for advice before.

A year ago I bought a 2005 Sierra 2500HD Ext Cab with the 6.0L Vortec from my boss, got it for a good price considering it having been his beater work truck for two years, ended up needing the front end to be rebuilt and since then it's been pretty reliable.

When I bought it, I immediately noticed a howling noise that happened at cruising speed, at exactly 1500rpm and again around 2000-2100rpm.

I was running 245's on it since i bought the truck, but recently put on some 285's, which unfortunately brings my regular in-town cruising speed to exactly 1500rpm, and it's started getting extremely annoying.

The sound itself, when you sit in the cab, sounds like it's coming from behind the cab; but a friend of mine swears its coming from under the cab. It's a sort of howling/metallic vibration sound that happens once the truck is warm, but seems to subside when its hot or completely cold.

I can rev it to 1500rpms and put it in any gear, it happens in all of them. That tells me it's not transmission or differential related, unless it's some kind of bearing at the input of the transmission.

In fact, it's happened for so long I don't think it's a bearing, otherwise I expect something would have blown by now and it would be happening when it's cold. Theres someone else in my town with an '02 Suburban that does the same thing, and he says it's done it since he owned the truck, and thought it was normal for the trucks.

Another friend of mine suggested that it could be a cracked exhaust; but I don't want to sink too much money into an exhaust unless I know it'll get rid of the sound. This makes the most sense to me, since all the plastic/rubber exhaust hangers are worn out.

Any ideas?

servantsalesmen · March 25, 2015

My 04 extended cab 6.0 definitely has a houling sound around 1500 and again at 2200 ish. My guess is that there is some component with a natural frequency that resonates from the engine vibration. Mine has done it since new and it's never caused a problem.