Every time I rest my hand over the drive bay, my mac gets all pissy and makes an odd clicking noise.
May I additionally add that I use a SSD so it cannot be a dying hard drive. I tried a restart, to no avail. Also, no need for Laymen's terms.

I have a mac book pro 15',i've only had it for 7 months or so...it just recently starting making the clicking noise also..mines when i open it to use it.

My macbook pro 13 inch makes this same noise. I am thinking it is the hard drive impact sensor locking up the hard drive. I think they call it a free-fall sensor. It is used in the case that you drop your laptop on the floor it will lock up the hard drive so it is not damaged. Not sure if you should hear this with an SSD drive since their are no moving parts. It could be the sensor making the noise still though. http://www.derangedgeek.com/boost-your-pcs-performance-with-a-ssd.php