Take cover off and try and spot where sound from. Use a plastic ball pen or similar to stop fans, one at a time for a few seconds to see if making the noise. You can put the sharp end of a screwdriver against hard drive etc while putting ear to handle to hear if majing the sound.
a booming noise, hmm, nope, i don't think there is a single component that can make a noise like that. However, i think i know the cause, gremlins, that is right gremlins, clearly one has lodged itself somewhere and is wanting help from yourself to let it free.
if it is not that then it is probably the headboard of you parents bed hitting the wall.
