Knee swelling

I have a small swollen place on the outside of my left knee cap.  No pain with it at all though.  Just a little place that's squishy when I push on it (sorry, best description I can come up with).  Is this something I should be worried about?  I hate to waste a trip to the dr. on something like this when there's no pain.  Also, it's hard to tell exactly how swollen it is because this knee has been slightly swollen ever since my ACL surgery 7 years ago...but this is definitely a bit more than normal.  Any thoughts?