Chosen Solution
My wife’s MacBook Pro was dropped a while back. Ever since it has made a low humming sound that drives me crazy. It seems to be coming from the right fan and indeed sounds like a rotating noise. The heat sink was damaged in the fall, and I have already replaced that. I was hoping that would fix the noise, but it did not. While replacing the heat sink, I also removed the right fan, inspected it for damage, and cleaned it thoroughly. I did not see any damage. I need help diagnosing the problem so that I know what part needs replaced. I can easily replace the fan, but I am afraid this is not the problem, since I cannot find any damage to the fan. Any help would be greatly appreciated.
Diagnostics on these kind of problems can be both easy and frustrating at the same time. Luckily one thing is certain: the only thing that can cause a noise like that is a mechanical part. Since the MacBooks only contain a few rotating/moving parts, the diagnose is easily procured. The fan is indeed suspect number one: a slight imbalance in the blades is very hard to spot, but can easily create the noise. The bearings can have a similar problem, and aren’t even visible from the outside. I would try to get the machine running and gently stop the fan with your finger for a very short while. It’ll tell you enough to hear if it’s the problem. If it isn’t the fan though, repeat the process with all other moving parts, including traditional hard drive if still present, and replace accordingly
