Chosen Solution
One of the fans in my iMac has become very noisy (rattles). I suspect that the optical drive fan is the culprit as source of the noise is from the right hand side. However, the noise is continuous which is odd for a device which is only activated when a disk is inserted. According to smcFanControl the ODD is running at 1400rpm even when no disk is present. If I increase the fan speed to over 2000rpm the rattle disappears and the noise becomes more “fan-like”. How can I diagnose my problem further?
The only real way would be to open up your iMac and listen in on which fan is the noisiest. That is what I would do if my iMac had a noisy fan. Here’s some links for when you do find the culprit fan. iMac Intel 21.5" (Mid 2010-Late 2011) CPU Fan iMac Intel 21.5" (Late 2009-Mid 2011) Hard Drive Fan Optical Drive Fan Replacement part iMac Intel 21.5" EMC 2428 Optical Drive Fan Replacement iMac Intel 21.5" EMC 2428 Hard Drive Fan Replacement iMac Intel 21.5" EMC 2428 CPU Fan Replacement
