This is a very very vague issue. I have had knee issues on and off since wrestling(shooting without pads tears them up bad). But it could be anything from an injury getting aggravated, to dryer joints, to a newer deficiency in something.
This is all IMO, I am no doctor.
How long has it been going since it started recently? I shanked my left knee with an ice skate in January(got a scar too). And it had sporadic pain for about 6 months and still pops during squats now.
Does it pop, feel like its grinding any, feel like its a tearing/pull feeling, or a sharp stabbing pain....
I hate identifying pain, its hard alot, but honestly its the only way to get a better idea.