So I've sorted all the niggles on the car since getting it a few weeks ago. The last issue I have is a noise that I'm not sure what it is.

In any gear, if I ease off the throttle to the point where the accelerator pedal reaches it's starting (resting) point and the car starts to slow due to engine braking, there's a loud rattle that sounds like it's coming from the back of the car. It happens when I reapply the throttle too, i.e. as the accelerator moves off it's resting point and the car accelerates. It disappears within about a half a second. It literally only happens at the point where I come completely off the throttle, or go back on the throttle.

For example in both 2nd, 3rd and 4th gear I was driving at a constant 4,500 - 5,000 RPM. Lifted off the throttle, and at the point where I was completely off the throttle there was the loud rattle from the back for about half a second. As soon as I give a touch of throttle again, the rattle is heard again. It's only the transition period between on and off throttle when it's heard.

The best description of the sound I can think of is turning on a food blender that's filled up with ice blocks.

When I'm on throttle there is absolutely no noise. I'm pretty certain it's coming from behind me. Could it be the diff? Drive shaft?

I've changed all fluids in the car in the last week.