Triathlete (now having to retire) since developing psoriatic arthritis in the knees has begun to suffer from pain behind the knee when:
Deadlifting
Kettlebell swing/snatch
olympic clean/snatch
… in the mean time, foam roll your thighs thoroughly all around starting just above the knee and going all the way up your thighs before lifting EVERY TIME YOU LIFT. Foam roll the back and sides of your calves, too. Take at least 10 minutes and do a very thorough job of it. Do it in between lifting, too, on your rest days.