I am having the same problem with Thermaltake Spedo's side fan (TT-2020). It seems that perhaps one of the ball bearings is loose and is causing the blades to hit the vents.
I do not know if you can do it with yours, but I plan on going to a hardware store and buying some longer screws and using an extra nut or washers to move the blades away from the vents that they are hitting.
Edited (sorry for the later posts):
FYI the solution for mine worked only because it was not an enclosed fan.
It looks like yours might be, or possibly has a barrier behind it from the case. Is there any space to move that gray grating behind it? That's what it is hitting because the blades are not spinning as aligned as they should.
Note: the fan has not gone "bad", but it is damaged. Worst case scenario you have to replace it, but typically it can be fixed.
Sorry to keep posting on your thread, but here's another suggestion:
When you held your thumb to the top-right side, it got quiet. The screw holes appear to be on the top-left and bottom-right. Take a drill and put another hole in the top-right and put a nut on the other side. You would want a 8/32 ... perhaps 1" or 1/2" machine screw and a nut.
Also, as a front fan, that grating is only to protect the fan from "debris". Fur, dust, etc., from hitting the fan. You really need to worry more about any intake fans you may have in those regards. Worst-case scenario, cut out that case grating with a Dremel or other tool. It actually would help clean out your case, although you would see a lot more crap piling up on the front and have to clean it more often.