It sounds like one of the bearings on the blower fan may have gone bad, in which case they are fairly simple to replace. If you are mechanically inclined, shut the power to the furnace off and remove the cover on the blower fan and try turning it and moving it up and down by hand. There should be very little to no play in the fan and it should turn smoothly. If not, remove the offending bearing and take it to your local hardware store or hvac supply and they should be able to match it up. You are more likely to find this part at a locally owned hardwars store, such as an ace hardware, than at the big box stores like home depot or lowes.