Volvo Repair: Drained Battery, s60 volvo, somwhere

Question
I just Purchased a 2001 S60 Volvo with only 25000 miles on it. I am not at all familiar with Volvos this being my first one.

One morning my wife tried starting the car and the battery was drained. There was either a buzzing sound or a fan just barely running. The sound seemed to be coming from the driver's side of the dash. I recharged the battery and have not had the problem since. I'm sure this didn't heal itself and will happen again. I would appreciate any advice you could give me.

Answer
Harold, There is a draw somwhere and with these cars I cant really tell you what to check because the car is all computer controlled and needs to be scanned by a Volvo shop or Dealer.  If you need help finding a shop I will be glad to assist you.  Roger