strange crackling noises coming from inside

so i got an iMac that someone gave me, and sometimes it makes weird crackling noises they seem to be coming from inside of it, and it does them only when powered on, it's not that loud and it seems to be coming from behind the screen mostly where the psu is located, but i'm not sure...

§the mac works perfectly though, no flickers, no sudden shutdowns, no weird smells, i heard that it could be an audio issue, also that a capacitor on the psu can be failing and cause the problem, as of the location of the crackling noises the psu is the most likely thing.

but will i have problems in the future if i keep using it like it dying on me randomly? i had a psu from a 2006 imac explode on me once and i don't want it to happen again on my 2010, i do have another psu from a 21.5'' 2009 imac of the same size, last time i tested it it worked, so is it compatible with the 2010? also if the current psu dies will it just die or damage other parts of the system?