rumbling and knocking noises

Hi all
I seem to have a problem with my c30 when i am decelerating i can hear a rumbling noise coming from the floor no matter what speed i am doing.

It is nothing to do with the engine because the noise doesn't change with engine speed.

I have had the car on a ramp and the problem goes away however when i put the car back on the floor the noise starts again so it might be a driveshaft issue with the inner boot however i do have a feeling it could be one could be the diff on its way out which i really dont want but could it also be a wheel bearing issue?

thanks in advance.

Usually with wheel bearings the noise changes depending on what speed you're doing, you mention it happens at all speeds but does the noise vary with the speed?