There are 3 major kinds of sounds:

popping is usually air in the joint.

snapping or cracking may be a tendon moving or slipping

grinding is called crepitus and involves friction in the joint and
is most common with arthritis.

These are only general descriptions, because popping and snapping may sound alike. Usually the snapping you can feel more than a pop. I find popping to be mostly painless.

My right knee has been pretty bad the past decade. Right now it is okay... but it never popped using stairs. I can pop it in bed however, by flexing it-- Seems it is very unstable to side to side motion, and in bed we may press on the lateral aspect and slightly move it out of alignment.

Most of my knee inflammation (MRI diagnosed synovitis), responded to SAMe. I took that for several years with great success.