Brakes thump when apllied
 

this problem has come and gone and now is back..what changes
first got the car had std rims with crap tyres, removed all and put a good spare set of std rims on with as new tyres, no issues..
have now put on new mag wheels/tyres no shudders or vibes but when applying brakes gently or not ..just tapping the brake pedal you feel and hear a thump [feels like torque converter, and seems to be from the rear ] ..very consistent does it every time but not at low speed ..anything over say 50kph..in gear or not
sticking brake cailper ?, rotors appear to be fine..
I even removed each wheel and put back on in case wheel nuts on too tight ...baffled ??:confused:

Dave