Laptop hard drive makes strange noise, but only when plugged in.?

Question

My laptop hard drive started making a strange intermittent noise like cellophane being rubbed together, especially when booting up or coming out of sleep mode, but also during use. It sounds like the last failing hard drive in this video:

http://www.metacafe.com/watch/323388/hard_drive_failure_test

So, I thought my hard drive was going bad. But I noticed that the instant I disconnected the AC power (ie, I switch to battery), the noise stops.

I don't think the sound is coming from the speakers like interference. It sounds like it's actually coming from inside the case. Though, since it's a laptop, it's hard to tell. Muting has no effect, but if it's interference, I'm not sure if muting would make a difference anyway.

Any ideas? Should I replace the AC power?

Thank you!

Answer 1

That is probably the reading head going back and forth. You might just have a very fragmented disk and going to battery mode tries to keep the disk from spinning up too much. Try defragmenting and if that does not fix it, it might be physically failing.