under car knock on accel/decel

Hi all,

I've recently noticed a deep sounding knock from underneath my car, usually between when I decelerate for a corner or lights and then accelerate away. I haven't been pulling away too quickly (£1.30 per litre/$7.50 ish USD per gallon soon makes you watch your speed ..... now and again) or throwing my car about like a 17 year old in a Corsa. It kinda sounds like it's coming from the back right hand side of the car. Does anybody know if this could perhaps be the diff, brakes or a bit of play elsewhere? Anybody else experienced such issues? 2002 330ci