need help please

[72kool]

im in need of some opinions on what to look for. while driving down the road i feel a bad knocking/thumping in the driver floor board next to the dimmer switch. it feels like something is banging on the floor board and only stops if im on the brakes.there is nothing actual hitting the floor thoe and nothing looks out of place or loose.ive checked the brakes and shocks (new) and wheel bearings and ball joints. any ideas? ive run out and dont know where to go from here. thanks in advanced