Screeching noise turned out to be a bad fan
My MacBook Pro had begun making an intermittent screeching noise after I accidentally dropped it. It only fell about a foot and a half but it was enough to damage something. The noise sounded like the tone of an an old fax machine, almost like the hard drive was girding away at a high pitch. The computer never ran hot and every diagnostic seemed to show everything was working however the noise was driving me nuts.
I started experiencing all kinds of crashes lock-ups and unexplained weird stuff so I figured it HAD to be the hard drive. I replaced the hard drive with a Samsung Solid State Drive 830 Series and increased the RAM to maximum. Incredibly easy to do and I figured the noise would be gone. The MacBook booted up faster than ever and within seconds the noise started up again.
I took off the back off of the computer, laid it in my lap (making sure no keys were getting pressed) and watched the insides of the machine as I turned it on. I was surprised to see the Right fan jerking around but not spinning and the noise was not actually coming from the fan (which was not working properly). The noise was intermittent feedback. You see, the computer kept trying to send a single to the fan to spin. When the fan would spin there was no noise but most of the time the fan didn't work so there was this high pitched feed back noise coming from the computer. Every time the fan would fail the noise would sputter and sound like grinding. When the fan completely failed to turn the noise would remain constant.
I ordered a new right fan as well as tools to repair my computer from iFixit.com, followed the installation instructions and process took mere minutes. No more noise and now my MacBook Pro runs faster than ever… and it's completely silent. Repairs were a breeze.
Do yourself a favor and do not try to second guess what might be making a noise or causing a problem (Although I am glad I upgraded to a larger SSD hard drive it might not have been necessary in my case). Take a look in the computer and be sure you know what's wrong before you purchase anything. Also, be sure you have all the correct tools to do the job and if you are not sure spend the few extra bucks and get what you need to do the job right.
MacBook Pro 15" Unibody (2.53 GHz Mid 2009) or 17" Unibody (Early/Mid 2009) Right Fan