I've been struggling trying to get reliable altitude data for my quad.  Whenever I try altitude hold, it'll continually rise or fall, but not hold any sort of steady altitude.  In testing I've let it get to the point where it landed and where it rose over 50ft after engaging altitude hold.  Here's my config:   Standard 3DR Quad kit with electronics (APM1 w/oilpan) MB1200 XL Sonar with power suppl…