External Hard Drive beeps and freezes

Hey everyone. I had an External Western Digital Ultra IDE hard drive hooked up to my Ibook G4 via USB. The drive was working fine with no problems for several weeks. It started giving me problems with I formatted my Ibook and then reconnected the hard drive. (I'm not sure if this is related though) Thing is, the drive works great as long as I'm continually accessing data from it (i.e. playing music non stop), but if I am not pulling stuff from it, after about 2 minutes it starts to make beeping noises and the blue light that is usually lit up on the enclosure goes off and then I can't access the drive at all. So I just have to turn the power off...turn it back on...and it's fine...as long as I'm using it. I don't think its the hard drive because it works fine and no data lost as long as I'm using it. Could the enclosure be blamed or perhaps could it be some kind of power settings...like it is going into hibernation or the like? Please help!!!!