It may be that we have had similar problems. One of my drives sounded like it was continually sounding like it was being accessed, making a noise very similar to when I boot it up.
What worked for me was a defrag and drive cleanup, now it has returned to a more normal purr with the odd check sound every now and again.
(Not telling you how to suck eggs but backup first, and set restore point, just in case something goes awry)