The way you describe the noises your PC makes sounds to me like you have one or more cooling fans that have loose, worn bearings. The fan shafts wobble around inside their "bearings" (actually sleeves impregnated with oil that eventually goes away and leaves the sleeve bearings dry). Only more expensive cooling fans have real ball bearings in them.
There's a novel fix for this. Open the cabinet and remove the fans from their mounts or heat sinks. Note the position of the air flow direction arrows on the case of the fans. Turn the fan over and notice the decal stuck on the hub of the fan, and carefully lift one side of the decal. If you completely remove it it's okay, but you want to put it back in place if possible. Next (this is the novel part), dip the end of a toothpick in a light oil - olive oil or vegetable oil will suffice - and let one drop of the oil fall into the hub of the fan without letting any fall to the side where the decal was stuck. There's nothing wrong with a second drop, but believe it or not, too much oil can cause excessive friction and slow down the fan speed. You want to lubricate the fan sleeve bearings, not drown them. Now stick the decal back in place to keep dust out of the fan motor and bearings. Reassemble everything (you did note the way the arrows on the fan pointed, didn't you?), cleaning out any loose dust bunnies and woolly boogers while everything is pulled apart. Power up and see if the noise is lessened or gone.
I've done this several times. It works - IF the racket is caused by loose fan bearings. What the hey, it's worth a try.