Need help, had rear brake pads fitted (been told no problems with them) O/S suspension arm fitted (been told no problem with that) and ever since I reverse backwards and brake and then forward and brake and then the clonk noise appears, anyone heard of this before? 

Now that could be both suspension or brakes

Brakes is more like a clicking noise if the pads are moving in the carrier but if the caliper is loose then this will also make a noise
Check the caliper is firmly secured it will flop around and you will hear a clunking noise if not

If you place a wheel wrench on the wheel nut and move the car backwards and fowards with it that should narrow down the are of the noise