Every once and a while, when I shift my car from P to R, or P to D, I will get a loud bang coming from the floorboard. I'm guessing it could be my y-pipe hitting the floor, but what would make it do that? Broken hanger, bad motor mount ??? I'm still on the factory headers and y-pipe. I'll be swapping the headers for SLP mids and a RandomTech high-flow dual-cat y-pipe this spring. This bang only happens when I'm shifting from P.

 

Yeah my buddys camaro did that after he installed headers though and it was his motor mounts, so I guess it could be you motor mounts I don't know with the stock manifolds and y-pipe though. Might be loose hanger or something like you said, but maybe someone else will know how many miles on the car?

 

check the tranny mount first

 

this is more than likely it
also check u-joints

 

I have a poly trans mount installed in the spring. So it shouldn't be that.