£4,500 I'm told for the interior mods when it was 12 months old. It was a motor related noise of sorts, and it didn't persist after say 5mins. I suppose this fits with it being air suspension related, I just couldn't figure why it would be coming from the struts perhaps and not the compressor, but Terry mentions the noise could just be travelling up the chassis to the engine bay, which seems plausible. I don't mind getting my hands dirty so I suppose I could always try swopping the compressor (buy one in anticipation of it failing at some stage anyway) to see if it cures it. First thing to do I suppose is next time I run it, keep it stationary and get my head under the bonnet to try and locate the origin of the noise(s)