Ryobi 12" CMS making odd sound

I have had a Ryobi 12" CMS for about 2 years. It has just started making a grinding noise when it stops spinning. It only happens when it is run for more than about 6 seconds; just a quick on and off doesn't make the noise. Sound and works fine.
Any idea what it is, and if it matters?
Okay, it is my own fault for buying a Ryobi, but since I have it and it seems broken, lets go from there.
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