USB disk disconnects randomly
I'm experiencing an annoying problem with my external USB disk. At random times (these can be short or long periods), it starts making some noise (like when it's intensively reading or writing) and then it vanishes (like if I had unplugged it). Of course, the system complains with a message like "You have not ejected your disk properly...".
Sometimes it happen 3 minutes after I turn the disk on, sometimes it happen after some hours of use.
And, in the Console, I don't see anything useful (only mds stating "Media not present", but that's obviously after the problem).
An idea what I can do/check?
(P.S: I hope to be in the correct discussion board: the Leopard board had "internal errors" and I could not post there).
MacBook Pro, Mac OS X (10.5.6)