Noise coming from right side of MBP (HD, fan, or ???)

[Paul B]

Occasionally, there is a noise coming from the right side of my MBP.

It's like a short buzz and it repeats every second or so for a few minutes, then stops and returns to normal. This happens maybe once a day and only started happening recently.

I was worried that the disk might be failing but according to this link, I don't think it would be classified as a hard drive failure.

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My MBP is a 17" Penryn (early 2008) with a 200GB Hitachi HD. SMART status in Disk Utility shows "Verified."

The only other thing I can think of is the cooling fan but I'm skeptical, given that this only started happening recently.

Any ideas? I've already backed up my system just in case but I'd like to find out what's causing this and fix it.