I have a Late 2009 iMac 27" i7. The GPU is failing and I am going to remove it and bake it. If I get another year out of...

I see that this is a question from 2015. Back to the future in 2022, I had the same problem, a knocking sound as the turntable rotated. With the turntable removed, no noise! I cleaned the roller track as per previous answers and the noise disappeared. Good question, correct answers! Many thanks.

I have the 2374. I baked the graphics card two months ago and it restored the computer, but of course it may fail again. If I get a year out of it I'll be satisfied. I agree with the other responses that it's likely a poor investment to sink much money into this model.