Apple MD094LL/A manual P04, From fan housing, Reinstall fans while carefully Yes

7.	Remove fans and rotate	Yes	Go to step 8
	blades. Verify if fan blades spin
	smoothly without interference	No	Replace affected fan.	P04
	from fan housing.
8.	Reinstall fans while carefully	Yes	Noise issue resolved. Suspect	P04
	ensuring that there are no		issue caused by interference
	cables routed under or near		from wiring or possible
	fan assembly that might cause		distortion or fan housing
	interference with fan blades.		when installed in system.
	After reassembling system
		No	Go to step 9.
	verify if noise issue is resolved.
9.	Temporarily remove LCD	Yes	Identify, inspect, and if	P04
	display then power ON system.		necessary replace part that
	Verify if source of noise can be		caused noise issue.
	located. Caution: The exposed
	power supply poses a serious
		No	Go to step 10.
	shock hazard. Take proper
	precautions when working
	around an energized system.
10. Disconnect these major		Yes	Identify, inspect, and if	P04
	modules/parts (hard drive,		necessary replace part that
	optical drive, fans, LCD display)		caused noise to disappear
	one at a time then power ON		when it was disconnected
	the system. Determine if noise		from the system.
	issue goes away when one of
	the modules is disconnected.
		No	All parts verified. Verify that
	Caution: The exposed power
	supply poses a serious shock		correct symptom flow is
	hazard. Take proper precautions		being used.
	when working around an
	energized system.

2010-09-09 iMac (27-inch, Mid 2010) Symptom Charts — Mechanical  120