Clicking and other delays you described could be signs the hard drive is failing. If you wanted to replace the drive and wanted to supply your own drive, you'd need to bring it into an Apple Authorized Service Provider, as the Apple store wouldn't replace a drive with one you provided.
However, I'd be more inclined if either of the tests above indicates a problem, to take it in and let Applecare replace it. Note, when Apple replaces a hard drive under warranty, they keep the old hard drive as a trade in. This bothers some people due to private data on the drive.