Early 2009 iMac freezing and ticking

Computer: Early 2009 24" iMac 2.93 GHz Intel Core 2 Duo with 4GB of 1067 MHz DDR3 and a NVIDIA GeForce GT 120 256MB and a new WD 1TB Black HD.

Problem: iMac has been freezing and repeating an audio ticking noise.

First occurred: After updating to Mountain Lion over a year ago, but has gotten more frequent. This occurs when I'm streaming TV shows or movies online, or when I'm playing graphics-intensive video games.

Since this started, I've tried resetting the PRAM, replaced the hard drive (old one was also a Western Digital), done clean reinstalls of the OS, tried Mavericks and Yosemite, with additional clean installs of those OSs, but the problem still persists. It is now to the point that when it freezes and starts ticking, I do a disk verification after reboot. Some of the time, it comes out OK, but more frequently, it results in a failed verification and failed repair, causing me to erase, reformat and reinstall all over again. I've even installed Temperature Guage Pro so I can monitor all the temps and manually control the fans in case it was a heat issue. Nothing's overheating, and it's still freezing and ticking.

Does anyone have any ideas?