Exhaust "humming"

[tshryock]

I have a '99 Dodge Dakota. The catalytic converter had the guts break loose on it, but it was a warranty repair. The exhaust pipe(s) and muffler from the cat on back were also replaced at this time (had to pay for that).
Now I have what sounds like a metalic "hum" or tone, best described as someone using a tuning fork -- this happens mainly around 30-40 mph. Obviously something isn't quite right with the new exhaust installation and something is rattling at a high rate of speed against something else.
Do you think this is just a matter of tightening up some bolts, or something else? I can handle the bolt tightening, but hate the hassle of having to take it all the way back to the shop if that's all it is.
It's hard to tell exactly what part of the exhaust is the culprit, but while driving I'd say it's coming from somewhere in back of the front passenger seats (I have the extended cab) -- maybe about where the cab and bed meet.
All help suggestions appreciated.

Todd

[BleedDodge]

Crawl under there and grab it and yank it around. You're bound to hit some other part of the truck if it is actually hitting something else, and when it does, you'll be able to tell where.

[BamaDodgenMX]

Yea, I had the same problem when I had my custom exhaust done. Living on this bumpy road, it was bound to come a bit loose sooner or later. Right when the exhaust would sound the best and deepest, the pipes would vibrate and hum. Like Bleed said, just crawl up under your truck and nudge the pipes. Remember, even though they are hollow, they're also pretty strong (hopefully) so don't worry about having to be gentle.

[tshryock]

Ok, crawled under it Saturday. Everything looks like it's installed properly and yanking it around causes the exhaust to hit absolutley nothing.

The noise started when the exhaust system was replaced, so I assumed it was that.

So, here are my two theories:
1) It's the exhaust vibrating at such a high rate of speed it's resonating. Based on where it sounds like it is coming from, I'd say it's would be either the muffler or the tailpipe assembly. But I'm not sure how I would fix it.
2) It's something else. But there's not much else under there.

Any one have any ideas?

[stanbell]

Might be a heat shield vibrating