There was a slight rattle coming from my furnace fan. I opened up the intake grate, saw some screws gilding the fan to the bottom of the cage, and proceeded to tighten them. Now there is a new noise that sounds like some is off kilter or out of alignment - like a low far off helicopter noise. I then tried to untighten the screws a little since I essentially caused the issue by tinkering with it so I figured I could go back to where I started. Any suggestions?