GTLimited02

Hey all, New to this web community, I'm liking what I am seeing. Anyway, I have a 2002 Legacy GT Limited (2.5) with 44,500 miles. I've noticed, especially in warmer temps with the windows down, a significant knocking in the engine around 30-40 MPH...I took it to my dealer and they said after driving it, they heard it too, and recommended I up my gas octane. So I switched to 89 octane from the MFR recommended 87, which helped a little but it still makes the knocking/pinging sound. I heard somewhere that this is a recurring problem on the 02's, and that the 02's are also prone to blown head gaskets down the road. I am hoping this is not the case. Plus It just blew a headlight and that irks me because in all the cars I have had, all of which ended up with over 100K, none of them ever blew a bulb, nevermind a headlight. Maybe I am expecting too much, but I never see other Subes with blown headlights. Hopefully I didn't get a lemon! Any input you all have would be greatly appreciated. Thanks!