I have an early 2011 MBP and opened it's back more than once, to replace RAM, HDD and 2 weeks ago I installed an SSD. For some time already I hear a faint ticking noise from the body when the laptop is running, laying on a flat surface. First I thought it's the HDD's head hitting an end position, that was part of the reason I replaced it. Now with the SSD I still hear the noise sometimes.
I could not figure out what it depends on, sometime it comes and I hear 1 tick in irregular intervals form 1 to 5 secs, sometimes I hear a lot short after each other, and some other times the noise is not audible at all for hours.
I have the impression that the noise comes from somewhere below the trackpad, around the place of the HDD, now SSD.
Any idea what that could be?