A Question About Knees

I don't want to make a mountain out of a molehill but I thought I'd ask this question.

I've had some knee problems (pain when bending the knees or walking downhill) when I was a lot younger, mostly when I used to go cycling, but I haven't experienced any of those issues for a while now. However, about 2 weeks ago, my knees started popping every time I straighten my legs after sitting with my knees bent for a while. It's not painful (at least not yet) but it's really unpleasant, quite loud and it's new. I've never had this problem before.

I've done several programmes in the past 6 months and I can't say that I have overexerted myself. It could be the start of a cartilage problem but I don't really want to make an appointment only to waste the doctor's time by announcing that my knees pop...

Does anyone have this or similar issues? Thank you.