How to catch a weakest link in a RAID pack?

[P3rv3rt B3ar]

This is not really XL related prob, well besides fact it appears on my htpc, but i wanted to exploit the knowledgeable crowd here:

I have this sporadic prob that causes HTPC to slow down for a while/ hang /BSOD/reboot (sometimes with even data corruption) its always accompanied by this harddrive noise, not particularly alarming noise, but sounds like drive is trying to move the arm but is kind of too tired or something like that That makes me speculate that one of the drives on my 4 drive striping pack is approaching its retiring mileage.

Only question is just how will lazy bear, with least trouble approach, identify the bad apple?

Note that its striping pack so i just cant go on easily replacing them one at the time with new drive and see when problem vanishes.