I bought a 2004 A8L with only 67k miles "as-is" from a dealer two weeks ago.

Since bringing it home, the compressor on the air suspension seems to be getting more noticeable (hum, vibration in cabin) the more I drive the car. It really takes away from the enjoyment because when it's not on, the car is smooth as silk.

Not only that, now there's a sound coming from the dash when the compressor is in operation that only adds to the annoyance. The sound is electronic in nature, and is not unlike the sound a hard-drive makes on an old PC-- just higher pitched. It sounds like computations are being made. Either that or it's a mouse playing a miniature xylophone as fast as he can.

Question 1: Is this the Air Suspension's "central control unit" that I'm hearing and is it failing (the sound always goes away a split second before the compressor shuts off)? If so, cost to replace?

Question 2: Is the compressor itself getting ready to fail because it's so noticeable? I can't imagine A8L owners being willing to put up with a noticeable air compressor just to ride on air. I'd rather have a traditional suspension than drive a car that feels like a seat massage that randomly comes and goes.