Flight out of Viola Fields in Carpinteria, CA. This was the first flight that I experienced compass errors possibly due to railroad communications/antenna interference?? During compass errors, P3P went into ATTI mode automatically and flight was feeling really unstable. First sign of instability was at 0:55 (see uneven horizon throughout flight) then turned around at 1:18. Controller kept saying "ATTI MODE, ATTI MODE" and flight was feeling even more unstable. I was finally able to turn it around at 1:45 for a landing.