Since my Macbook Air fell onto the floor, it has become somehow noisy. I just can't locate the source of that noise. It's either the Harddisk or the CPU-fan. But how can I actually find out. I opened the Notebook, and tried to listen closely, but still can't tell, which of the two components it could be.

So my question is: Is there any way I can turn off one of the two for some seconds. Turning off the Harddisk for some seconds, while the notebook is running, so that I can see if the noise will disappear? Or vice versa turning off the fan...

Any ideas how to do one of those two things?

Thanks in advance.

Boot thing without HDD???

Yeah, but before I try that, I want to be sure, there's no other options, like some tool or command to power down the harddrive for some seconds or something.

You can try resetting the PRAM. Boot the computer, then hold cmd+opt+P+R and let it reboot twice. After you hear the chime a second time, let go and see if it fixes anything.