I've been out of the game for a few months and just got round to installing 3.0.1. Testing it out today in the back yard it seemed to work fine until I switched to Alt-Hold. In Alt-Hold mode the just kept wanting to climb until I switched it back to stabilise.
I've attached logs from two of the flights where this has occurred. Below is a graph showing the behaviour (taken from 2013-08-10 00-16 1.log). For some reason the WPAlt keeps increasing while Alt-Hold is engaged, but I can't figure out why.
I am running an APM 2.5 enclosed in the 3DR case (complete with foam covering the baro). My sonar is mounted as far from the ESCs and BEC as I can put it, and has powerline filtering.
I have the APM mounted on squares of anti vibration foam at each corner. I believe the vibrations are within what is acceptable (IMU logging is turned on - see for yourself). Finally, not that I think it affects Alt-Hold, I get around 40% interference when running the compassmot test.
If someone could take a look and let me know what's going on here it would be much appreciated.