Engine/Transmission (1998.5 - 2002) Exhaust sound

[dfoley]

I have a strange noise with my 1998.5 24V. When I first start it in the morning all is well with the way it sounds. After about 5 minutes of driving it sounds like it develops an exhaust leak that I can only hear at idle. It's subtle like a deep rumble not a psst psst psst sound. I've searched all over the exhaust manifold for a crack and checked all the manifold bolts as well as around the turbo to manifold flange. When I pulled the big air intake hose off at the air cleaner "I left it connected to the turbo" it sounded like the same noise except much louder. I found no evidence that exhaust gas was leaking to that side of the turbo and don't even know if it's possible. The truck runs great and I found no slop in the impeller bearing. It has 358,000 miles on it with no major problems. This noise is driving me crazy, something has changed! Any ideas. I also checked the entire exhaust system.

 

[markmnj]

I had an exhaust vibration on mine that would show up only under certain speeds...kind of a constant low rumble like you describe at certain rpm's. Mine ended up being a loose hangar where downpipe bracket attaches to frame. I found it by laying underneath and smacking the pipe with palm of my hand and could hear a squeak. Fixed by repositioning the mount and tightening up everything. But a loose pipe or pipe rubbing/hitting/vibrating can be anywhere along the system. I have aftermarket exhaust FYI