i just had the same problem with my knees and u need to be extra careful. i just got finished with therapy for this happening to my knee and they told me that my IT bands were tight which is just a muscle on your leg that helps your quads move and helps your kneecap stay straight. as i said, i just finished therapy for this and im right now injured and my soccer season is blown this year. my bands were so tight that they actually dislocated my knee and bruised the bone inside. get on a bike or an eliptical trainer and start doing quad sets and excercises and u should be ok. it also might be good to go see an orthopaedic doc just in case! hope this helps!
could be just that you over worked them. Do you do anything like long distance running, jumping etc...regularly? I play soccer i had the same problem...i rested for a bit, taking it easy and it went away.
played basketball but not real seriously mostly baseball
sounds like bad knees to me. do you play basketball or tennis because it sounds like your wearing away your i wanna say cartiladge in your knee caps.