this is not a new development but more annoying now that I am going for performance sound.
There is a rattle the accelerates with the rpm's coming from just behind the motor. I'd almost say it was a loose heatshield if I didn't know better and it didn't change in time with the rpm's. Also when I get on the freeway and floor it 1st gear is nice but around 3k rpm's it drops 200rpms and then goes back up. I think my tranny might be shot but thought I'd ask

Do you guys have any ideas?

 

Your rattle could be a number of things. I'd just start poking and pulling until you find something loose. Assuming you have an automatic transmission, the RPM change is probably your torque converter going in & out of lock-up mode. Hard to say if it's a problem without experiencing it. If you've got the 5-speed, you may be in for some trouble.

 

Get under there with a rubber mallet. Never fails, bangin around will always reveal an external engine rattle. Try it, it works.