kmag has a good point... the lid of my box rattles a lot. If the box itself is rubbing against the wheel arch it will also generate a lot of noise. I've documented a fix that worked for me using a rubber mallet (optional) and a few fibre washers here http://paulp38a.com/99p38a/eas-valve-block-renew/
Thanks for the replys the mounts are fine and the rattle is still there even with the lid removed I mounting rubbers are fine and are nice and tight it sounds like its coming from inside the compressor
If you notice that the compressor itself is making the rattling sound, it may be worthwhile to take apart the engine side of the compressor and replace the 2 brushes as well as the springs that push the brushes into the armature. Sometimes, these things are not positioned properly against the armature, and cause excess vibration.
Another possibility would be that the bearings (I believe there were 2 in there) have gone bad-Though, this would be a less likely scenario.