Exhaust

[TTM]

I was wondering if you guys could help me out. I have a 94 6.5L 2500 and I got my exhaust changed last week. Now I have a humming noise in the cab only though when I'm stopped at a light idling. I got the stock muffler, tailpipe and the pipe running from the square flange down to the muffler changed(the cat was already cut out when I bought the truck hence the reason for the pipe from the flange to the muffler) I got the guy just weld the new pipe onto the square flange keeping the flange intact. The rest of the system regular install. I've checked the system out and all the hangers are working and everything is aligned. The truck runs fine other than that. Could they have installed the wrong muffler? Orrrrr??? :confused:

[Spindrift]

Check the entire run of new pipe. It's possible that your pipe is coming into contact with a frame rail, fender well, etc.

[TTM]

Checked that to; with the truck idling, and I've got about a inch clearance at the closest point in system and no contact. I was going take all apart and put it back together to see if that made a difference but the connections are to tight.What about the flange? When the cat gets cut out do you cut the flange out and weld to the exhaust pipe off the turbo? I just hate take back to the shop at this point to find out that's it's something simple.

[rj]

Your piping could have a natural harmonic frequency that is creating the noise. Changing the length between supports can change the harmonics. You might try adding one or more pipe supports (even temporary at first) to see if the noise goes away.

Good luck.

[diesel65]

Replacing the exhaust could be a coincidence but check your engine mounts, make sure the engine is not sitting on the chassis.

[David Brady]

I have the same problem when I installed my new system I have the resonance at idle speed. It was strong enough to vibrate the dash and make you want to roll down the windows. I installed my own pipe and believe the front mount to be stressed extra tight is causing the noise. But as I don't idle much I have ignored it and it is going away. If that rubber mount snaps I'll know for sure. I haven't actually noticed it recently, so it has reduced quite a bit over the last 5K miles. At first I wanted to modify that front hanger attachment to reduce the load but I still haven't done that.

[TTM]

Thanks for the tips guys, in my owners manual it shows that a hanger in close to where the cat was. As mentioned before I think the new pipe has changed the harmonics. I'll put a hanger in that spot first and see if that makes a difference.