Hi there!
Well, without a clinical evaluation it would be difficult to determine the cause of the bump. Possibilities that may need to be considered include enlarged bursa, fractures/ loose bodies, bony/ cartilaginous, outgrowths, growths from any of the soft tissues etc. You may consider getting this evaluated by a primary care physician or an orthopedician for an accurate diagnosis and appropriate management.
Hope this is helpful.
Take care!