I thought I'd bring up this question here since all the results I've found about similar noises have lead to it being a hard drive sudden motion sensor issue. There is an annoying tinking or clicking sound that happens regularly in the upper left hand corner of my 15" Early 2008 MacBook Pro. It is not anywhere near my hard drive. It seems to happen about where the escape key is which is also near where the fan is. I have determined that it is not the fan by turning the fans off and to full power using smcFanControl. The noise stays the same. The noise only occurs when I am not running anything processor intensive. As soon as I start something like SETI@home, the rate of the tinking quickly speeds up and decreases in volume until it goes away after a few seconds. As soon as I quit the program and the machine cools down, the noise starts up again. It is loud enough to be distracting in class, so I always turn on SETI@home. My assumption is that it has something to do with thermal expansion since it sounds a lot like the sounds a house makes when temperatures change. I have also just paid to have my entire motherboard swapped out a few weeks ago since my GPU died. The sound is the same before and after. Any suggestions or ideas?