500 series, making grinding noise from hub motor

[knharper]

I was able to fix the front wheel high-pitched whine with a drop of bike lube. It immediately went away completely. The grinding from the rear still happens from time to time, but not often, and mostly under "load," (ie, going uphill, etc.) I just avoid asking the bike too much! Not sure if it is a sign of something bad, though. Would love to know.