When I drive and my wife sits in the passenger side, the floor at the very front where she puts her feet near the firewall but on the floor, she feels a thumping vibration when I drive especially when I go over bumps. But it's a feeling she has and not a noise. Anybody have anyideas what it could be?

 

check the exhaust mounting, shields etc. Next I'd check the lower control arm bushings, shock mounts, sway bar links etc. Sometimes things like this are hard to find because sounds have a tendency to travel. I vote for the exhaust mainly because you changed it from stock.

 

Sounds like exhaust like he said have you had it off lately? Make sure the cat-converter is level to the chasis, you may have to looseen converter and either twist it or hold it up and retighten converter.