[Rotary Tool Issues]

I think I may have figured it out. I loosened the screws on the tool a little bit and it changed the noise. I think I just tightened the casing to much. Can anyone confirm that this may have caused the problem?

[Rotary Tool Issues]

I've been using my Chicago brand rotary tool for a project requiring sanding. After a while there started to be a grinding noise from the motor. Like something gritty was in the motor. I assumed it was a build up of saw dust in the casing around the motor so I would blow the dust out and the noise would stop. 

 

I thought the problem was solved. Eventually it got to a point where blowing the vents out didn't help. I was worried I'd burn out the motor if I didn't fix it. I unplugged it (safety first!) and opened the casing.

 

As I suspected there was some build up inside the tool. I proceeded to blow it out as well as I could. Once back together I turned it on. The grinding noise is gone but the motor's general sound it makes has changed. It's higher pitched then before. Not really a whine but definitely different then it was before.

 

I'm not sure what I did wrong. Nothing was moved when I had it opened. The best help I could find online said that it may need oiled, but it sounded normal before I opened it (besides the grinding noise).

 

Does anyone know what it might be?