scrubbing noise at 1300 RPM

[diandtom]

I have a scrubbling noise in my 06 LBZ Duramax at 1300 RPM. It will do it sitting still or moving. It only happens when the tach is at 1300. It is not very loud, but I can hear it. The truck has 55,000 miles on it.
Tom

[Ray,IN]

By chance has the coolant been changed or got low recently? Infrequently, air in the coolant system can make noises.

[sknight]

Can you expand on it some? Can you hear this noise from the drivers seat? Passenger seat? Outside? Metal scrubbing? Sanding noise?

[TandW]

Try cycling the AC and or heavy electrical loads to ascertain the effect the compressor and or alternator may be having. Bear in mind that a loose belt could be the culprit. Belts can behave badly without appearing bad. Good luck!!

[diandtom]

It does it sitting still or going down the road. I have replaced the belt , but it was doing it before I changed it. I have not changed the cooland. My wife can hear it as well as me. It makes no difference if the AC on or off. I wonder if it something to do with the turbo coming on ?

[sknight]

That engine had a varible pitch turbo that would suddenly make noise about then but it's more of a high pitched soft whistle than a scrubbing noise. That's normal, but I want to make sure that we're talking about the same noise.

I take it you just noticed this? Has any work been done recently?

[diandtom]

yes, I hear the high pitch whistle from the turbo, but this is something else. The scrub is not very loud, but you can hear it. It is constant at 1300 RPM if you can hold it there. I don't hear it when it comes back down from higher RPM only going up. The engine is a LBZ and is running fine.

[sknight]

That's strange. How about under a load like pulling your trailer?

On earlier models 2002-2004ish GM trucks were awful about heat shields buzzing especially the gas trucks. The shields would crack and cause a buzz while revving up but not coming back down and would do it at a very specific range like what you're describing.

I haven't seen many diesels doing that and no 2006 models (I left GM in 2008.) but that's where I'd look. Have someone rev the engine to make it buzz and walk around it, see if you can pin down an area.

Off the top of my dusty memory head they had shields on the head pipes going to the turbo, one on the pipe leaving the turbo and one on the muffler. The muffler was the usual culprit, it would crack at one of the ends and buzz like mad. It would sound like a scrubbing noise in some cases.

[diandtom]

It makes no difference pullling the fiver or sitting still. I think the fix is turn the radio up a little. I would never have heard this on my old 03 Chevy duramax as it had all kinds of noises.

[sknight]

The volume knob has fixed many minor noises!

Seriously it wouldn't be a bad idea to have a mechanic take a listen just to make sure it isn't something serious, I doubt they'll find much though.

Then turn the volume up to your favorite station!