Something is draining / discharging my battery

[anthonytexas]

2005 3.0I, 132,000 miles.

My OEM BMW battery finally gave out after 5 years. Kids leaving the interior lights on might have pushed it over the edge (although I thought my X5 usually shut everything off after a few minutes). Anyways, got the Advance Autopart Autocraft Platinum H7-AGM, 800 CCA with 36 months warranty. Two months later on July 1st, it was stone-cold dead! Couldn't even jump it. Took it back, the clerk verified it was dead, scratched his head, and got me a free replacement. Today, two WEEKS after the replacement, it was dead again! WTF? Took it back again and got another free replacement after some more strange looks from the clerk. What I've noticed:

1. I hardly use the X5 anymore for daily commute. My wife probably put 5-10 miles on it a day. Sometimes we don't even drive it for several days.

2. On both occasions, I noticed the high beam light on the driver side flickering. The passenger high beam was off, as with all the other lights. Why would that light be flickering? Was it activated a point overnight and we weren't aware? Is there a short circuited somewhere that could cause this?

3. I also noticed that the GPS DVD drive in the trunk constantly humming when I opened the trunk. Could the GPS driving be spinning and draining the battery? I removed the disc before, but I think the drive still runs at times. Tempted just to pull the power from the drive.

4. Sometimes (not all the time) the AUX fan continues to runs a good 3-4 minutes after the car is park and the keys are removed. This could be part of my AC issue, but could be a culprit?

Don't these BMWs shut all the power off after periods of inactivity? Not sure what other electrical components to look out for. Any advice is greatly appreciated. Thanks!