Thumping noise

Ok, I have a thumping noise when going over bumps very slowly, and also taking off kind of hard from a stop or slow roll. On hard take off it makes the noise repeatedly for a second and then goes away. Car is in my sig, just purchased last Thursday, previous owner did some suspension mods, it has after market springs and sway bars, and he says the springs are lowering springs.

Exhaust hitting??? Wore trans mount???? Wore torque arm mount???? Shock mount wore/loose???

Checked all of that and it seemed fine, but i looked at the car on a lift. Maybe i should put it on jack stands so the suspension will be loaded.