MyBook Starts UP at Will

Hello. I have an HP Pavillion running Vista Home Premium with a 500 G WD Mybook External

USB drive. I have it set for an automatic backup at midnight every night using Vista's backup

feature, which works well. The problem I'm having is that several times during the day when

I'm working at the computer, the external drive starts running, it slows my computer down

to a crawl, for 10 seconds or so, then it stops and computer returns to normal. 
Any ideas what's going on ? Not a big issue, mostly an annoyance.
Thanks in advance.


This is a normal behavior, the computer is checking the connected devices.

Thanks. Is there a way to prevent this? It interferes with my work as it locks up my comuter and I have to wait for it to finish.