Yes, my pain comes and goes too. Same, sudden movement, climbing downstairs, and after sitting or sleeping is when I feel it most.
I save all my aerobic exercises for the pool. Aqua aerobics does wonders for my knees and cardio. I particularly like doing exercises in water because it's low impact. I could jog and jump around in a pool for one hour and feel no pain during, or after. However, if I suddenly jump or run on a hard surface, I'll be out of action for a few weeks, from crippling pain.
Have you ever tried pool exercises (not just swimming, but full aerobics)?
It was my girlfriend from The Netherlands who had recommended that I try pool exercises when she came to visit me in the Philippines, and I've never looked back. Toning happens fast, and I particularly like that you gain long muscles instead of short muscles (compared to cycling or weightlifting)😁