The aircon on my Viano has a very noticeable burble/grumble to it. It is not a very loud noise but for some reason seems to be very penetrating; You seem to be able to hear it all the time, over everything. Before I start diagnosing, are other vans the same? Its more noticeable on the passenger side. It is there most of the time when the aircon is on, and is a deep grumble/burble/rumble noise. Unlike a bad bearing, the tone changes quite often. The aircon was regassed around 12 months ago (it was not in need of gas - done as part of routine) and made no difference to the noise.