iMac very hot, soft grinding noise

Hi there! I have an office full of oldish Macs and one iMac (27", 2009, Yosemite) in particular that is acting up. Performance wise it is ok- no unexpected shutdowns, but it takes a long time to boot and occasionally hangs on a white screen. Just recently I noticed that the top left corner/back of the chassis is incredibly hot- like can't-keep-your-hand-on-it hot. The fan is running but not overly fast. Pressing my ear to the chassis I can also hear a soft grinding, it's hard to tell if it's an HDD noise or a fan noise. The Apple Hardware Test gave the error code 4MOT/4/4000003 HDD-1343 which I didn't see much of online. I have the tools in house to attempt most repairs. Is this a hard drive error like the code suggests? Why so hot?

I ended up replacing the HDD fan on this machine using a little bit from iMac Intel 27" EMC 2390 Hard Drive Replacement and a little bit from iMac Intel 27" EMC 2309 and 2374 Teardown. Runs much cooler now!