Thanks for your response.
sperry, I might have to take you up on that offer.
Yeah, Nate mentioned the exhaust might cause some vibrations, especially when braking hard. I may try to look for pressure points and put some padding around it just to see if the noises go away. That would certainly be the easiest fix. I'll jack the car up when I get home and see what happens.
The differential is my fear. Those aren't cheap. At the same time, I think/hope the frame/exhaust is more likely since that's what's been worked on, and it's not like I'm making incredibly more power than I was stock. I've also tried not to abuse the car, though I do enjoy it.
BTW, the exhaust is Vishnu.