I've started cycling some long rides lately, and am feeling knee pain. It doesn't seem serious, but it's insistent enough that I've mostly avoided riding for a few days. When I do cycle, I do so at a high cadence, for short distances, and don't push myself.

The pain has been in various locations around the kneecap and also a bit at the back of the knee. Sometimes it feels like bubbles inside the knee, which sometimes pop (crack), other times just soreness around the knee in areas that don't seem to be muscles. The pain doesn't seem to have subsided significantly since I curtailed my riding activities.

So I have a couple of questions:

How much pain is an indicator that something serious is going on?

Does the specific location of knee pain indicate what's wrong?