It's not too much of an issue, but randomly my computer will make slight rumbly noises. I know this isn't caused by an overload of stuff, it's more to do with the actual case that all my technological computer hoo-hah is sitting in. I think it may be that one side is slightly loose and so it vibrates against the edge making the "rumbly" noise but it's completely random. Pushing something against the side stops it, but I don't want to constantly have to hold my hand there to stop the noise. Any suggestions?

So push something else against the side.

Nothing really works, it needs pressure against it

You should have someone with the correct know-how open the case and see what's loose, it might just be a cable from your power supply that's rubbing up against the side.

Assuming this is a desktop, try turning the case on the side and using your computer like that?

I'm afraid I don't have enough space to do that

Ditto, I'm experiencing the same thing. I tried pushing to the side and it eventually goes away. I'd say both of our computers are in need of some maintenance and upgrades.