Can anyone tell me the most likely cause of an intermittant rattle from around the aircon compressor on my 96 A4 2.6. The rattle is loud and only present when the aircon is switched on. The rattle is also intermitant and may not be heard for a week or two at a time. Is this likely to be the compressor, compressor clutch, or could the system only need re-gassing? Any advice welcome.