Bulging On The Knee With Pain, Difficulty In Going Downstairs, Relieves With Stretching Hamstrings. Have ACL In The Knee. What Is The Cause?

My left knee has what looks like part of a golf ball bulging out, I believe this is the top part of the fibula and my right knee has a similar knob but MUCH less obvious. I only noticed because I began having left knee pain after longer (10 miles) runs during my post-run cool down walk. It was very painful going downhill/stairs and I saw some suggestions of ITB issue but I have had that before and this was different. I have not had an ACL in that knee and am due to have some scar tissue (miniscus) removed later in the year. I haven t cut back on my running and the pain has lessened a bit, especially after stretching my hamstrings. My ITB exercises do a little bit but not much (adding to my above conclusion). I have a feeling it is just me getting old (42) but was wondering if this is a common thing that I just have not noticed before or if there is a condition this might be classified as. Thanks for any scoop!