"Thud" coming from underneath the car

Ok, so I have some weird thud coming from the bottom of my car. I just drove it for the first time since I put it in my garage for winter tonight. It ran fine, but I have a thud coming from the bottom. When I accelerate normally, up to about 30+ or so and let off, I get a thud. I'm thinking it's coming from somewhere near the tranny [automatic] or from the tranny itself.

I don't know if the previous owner installed a shift-kit or not, but I know the tranny is really strong under hard acceleration. I can chirp my tires going into 2nd off the line [but I think it's do to having the stock 245/50/16 Eagle RS-A tires]. I don't think one was installed, because I have all the recipts and paperwork from the previous owner, and nothing suggests any tranny work was done.

Also, sometimes when I'm slowing down to a stop, from say 40mph or so, I sometimes hear a thud coming from the underneath the car from the front. Could it be something suspension, tranny, or motor mount related? Or could the exhaust be hitting something when deaccelerating? The previous owner did have a Borla cat-back installed.

Any help?

Here's a list of stuff that I had installed last year since I took ownership if any of it helps. Prothane transmission mount and a 32mm front swaybar with polyurethane endlinks and durometer bushings.

check the torque arm mount located on the rear of the trans. see if you can pull/push the torque arm up/down.