So, I was away for 3 weeks on Business trip slash Vaca. came back to find that my 07 GTC has thrown a serious tantrum:
1. Battery was dead.
2. One of Suspensions was completely low
3. Now Car makes Loud humming sound as i drive, and it seems to increase with the RPM.

Going to take it to an indy shop few miles away ( came recommended by member on this forum).
but anyone has any ideas what am I looking at?

 

Is it possible the air suspension developed a leak causing the pump to run while you were away? This would flatten the batteries for sure. What you may be hearing now is the air compressor trying to compensate for a leak. It is worth noting that these cars are hard on batteries when the car is not running (alarm systems, etc.) and leaving it for three weeks could flatten the batteries without any other issues.

 

Dead in three weeks is not ok IMHO.

Gambit hope it is an easy cheap fix LMK.

 

As I think it through, my original suggestion was wrong. The air suspension pump will only work when the ignition is on. Therefore, it is impossible the pump killed your batteries. However, depending upon the ambient temperature and condition/age of your batteries, three weeks without charge could certainly leave them flat. Given that you observed a low suspension on one or more corners, it is possible the hum you hear is the suspension compressor (it is in the rear under the car beneath the license plate). If I am right about a leak and you do not fix it, the pump motor will eventually wear out. Are you getting any warning lights?