I can definately sympathise about knees - mine have been damage in two different ways by martial arts over the years and so they tend to be tender every so often. Its worse when there are weather changes about to happen - my knees ache way more then. Tends to be rather painful if one specific spot on my left knee has any pressure on it; have to be careful about the trousers I wear as a result of that.

When I saw a GP about it I was pretty much told that I was already doing the right things, that the muscles around my knees were very well developed and to come back if my knees ever locked.

I'd be interested to hear what they teach you in the knee class you'll be going to.