300td diesel,1984,noise in left rear wheel

[co.aulakh]

i have been having this recurring intermittant problem for the last 2 years.i renewed the emergency brake pads and it solved the problem for about 4 months now the problem has returned.
problem is this....... sometimes as the car gets warm the left rear wheel starts giving a thumping sound ,on acceleration.the noise goes away when the foot is removed from the accelaratoror when the car is coasting.
is it the drive shaft or the bearings,or the brakes..the sound is like something is touching as the wheel turns.
please help...its driving me crazy.if it was the bearings or the driveshaft would not the noise stay all the time.it is NOT a grinding sound....more like as if a hammer is being hit on a drum.