eSATA External hard drive issue

Just a quick question.....i recently just got the thermaltake max 4 and stuck my 500gb WD drive in there. After vista loads and i have been on my computer for about 15 minutes, something weird starts happening with the hard drive. The drive randomly spins up like an internal drive would when you turn your computer on and continues spinning for like 45 seconds. Then it will just stop and sound like its powering down only to start the process over again about 2-3 minutes later. Haha its really bizarre and its annoying the **** out of me while im sitting here. The power light is still on during all this and the drive isnt being accessed, just spinning. It quits doing it if i restart my computer like i said for about 15 minutes, it also does not spin up when the eSATA isnt plugged in to the mobo. i just ran the WD diagnostics quick and extended tests on it and it came back with no problems whatsoever.... Im wondering if its the eSATA thats causing the problem or vista....thanks for reading, hopefully i can get it figured out soon before i throw it at the wall lol