I've had a Cuisinart conical burr grinder for a year, but for about the last six months it takes forever to grind enough coffee for a pot. I've pulled it apart & brushed clean every surface and the shoot through which the grounds are supposed to fall. It just doesn't feed the beans into the burrs at the finer settings. No problem in the coarse range, but that's not how I grind my coffee. What's the problem?