As others mentioned, there is either a crack or (hopefully) a scratch on the right-side seat stay. down near the dropout. Check out the area on the rear of the frame, in front of the cassette where the axle goes thru. Can't tell from pics if it's just a scratch or perhaps a crack in the frame. If the frame is cracked, may as well stop work on the rest unless you just wish to try and salvage some parts. Hoping it's just a scratch!