you could have a program accessing it in the background. Say an av program is scanning the XHD when you plug it in. It could be for any number of reasons, good or bad. If your worried about viruses or malware just update your av definitions to there latest and do a full scan on all drives. If nothing shows up then i guess there's nothing to worry about. I turned on my xhd to copy/paste something i needed. Thats it, didn't use it for anything else. Then some time passes away and my xhd gives some kind of very long buzzing sound. XHD active light wasn't even flashing, so im not show if it was being accessed or not. After about a minute it stopped. :suspiciou