i have a usb hdd enclosure. i had one drive in there for awhile and it ran perfectly. i then switched another drive into it. this one was twice as large (40GB) and was also partitioned. now i've noticed that after the enclosure being on for awhile i'll hear clicks like when you're computer is restarting, and they'll happen more and more if i leave it on. pretty soon, i can't read anything from the drive and i have to turn it off and wait awhile before i can do anything to it.
what could be causing it to fail like that?