Maybe the bearings have gone? Most PSUs aren't designed to be end user serviceable and these days it is probably cheaper just to buy a replacement than to try and find someone who can fix it.
Yes but it's the hassle of changing it, it's in an awkward case.
Be more of a hassle if it went pop and took your computer with it. Ok there is not much chance of it happening, but it could.
How old is it? corsair PSUs are pretty reliable.
Desktop machine now powered by windows 8.1 pro 64bit, no dreaded metro, laptop by Linux