Hard drive acting odd, failing PSU the cause or is my hard drive about to die?

[Cheezus]

Alright, so just recently my PSU started acting odd, mainly the fan currently makes horrible grinding sounds constantly. Ever since that started, whenever I do something that involves the hard drive (copy/pasting files, deleting stuff) the hard drive makes two clicking noises about 2 seconds apart and then sounds like it spins down. During this time the activity light also goes out. Once that happens my entire computer freezes for about a minute before it clicks again and spins up. Most of the time I can resume whatever I was doing afterwards but a few times I've seen it get stuck in some kind of click, spin down, spin up loop over and over for 10-15 minutes.

My dad built this PC for me about 4 years ago, hard drive is a 750 GB Western Digital, Power Supply is a 550 watt (forgot specific brand, possibly a Goldenfield or some crappy Chinese PSU). Currently running Windows 7 Ultimate. I did an error check on HDTune and nothing bad came up, so it doesn't seem like the hard drive is going bad.

I don't really care if the hard drive or PSU fail because I've already ordered new ones, they were getting old anyways. All of my important data is already backed up. What could be causing this issue though?

EDIT: Just listened closer, and I honestly can't tell if the hard drive is really spinning down or if the head just stops moving during the time it's frozen.

[Cheezus]

Alright, it was the power supply. Just went and bought a cheap 465 watt PSU just to get me through the weekend until the new one gets here. It's slightly under powered but if I don't do too much it should last a few days. All of the freezing is stopped, grinding noise is gone and everything runs smoothly now.