Since this is a $7 fan and 99% of the time they are not a proprietary size, if you can mod it, do it. "Down the street" means a computer store that sells case fans.
There are usually these bizarre plastic-cutting screws that attach the fan to the case. If you can adjust them or put a piece of cardboad in to quiet it down that should be just fine.
From your description it could still be bearings or just the mounting. On nicer fans they make the fan rotate smoothly and silently. If the mounting assembly, which is probably an electric motor stuck into a plastic fitting, is off kilter the fan blades can be at an angle to strike the casing. So try to tweak it by changing that angle or "pushing on the center hub". Nothing too fancy, usually replacing the fan would work but if you can fix it it is even simpler.
What brand of PC or case is this. I have an Antec case, an Enlight case, etc.