My truck has been making a squealing noise. I thought it could be a boost leak at first but then thought it sounded more like a belt noise. We changed the tensioner and belt but did not help. I do not have a boost guage but it seams like the sound comes before it would have any significant boost pressure. It also makes the noise when the engine brake is engaged in fact it seams louder with the engine brake. I had my 12 valve for a long time and this is my first experince with the 6.7 and it seams like it has had alot of issues in the first 5 months I've owend it and of course it didn't come with a warenty.

 

I had a squeal that appeared when the engine brake was on and being used hard. It sounded like a belt squealing, and I could modulate its loudness with the throttle. The tech at the dealership looked at me like I was a bit goofy until he drove/experienced it. The source turned out to be a loose bolt on the egr cooler.

 

Thanks I'll have to look into that. I think it is due for a clean out anyway.