Lately I've been having a problem with random yaw in my hex where it wasn't before.
Two problems. First, it always wants to yaw 10-15 degrees at take-off, but I don't think it's a crooked arm/motor as it doesn't always yaw the same direction. In fact, the direction it yaws appears to be a function of the direction it's facing; if I'm facing north or east it wants to yaw clockwise; if I'm facing south or west it wants to yaw counterclockwise.
Second, there's mild yaw drift in flight. Again, the direction is not always the same, sometimes it yaws counter-clockwise and sometimes it yaws clockwise. In this case, the direction doesn't seem to be a function of direction the copter is facing, but the yaw is more likely to occur when I'm rolling or pitching the copter rather than just hovering.
I've tried updating the declination of the magnetometer, but that doesn't seem to solve the problem.
I've been flying the copter with this problem for 20-30 minutes a day for 3-4 days now, so I don't think it's a calibration issue.
Any suggestions for what else might be causing the problem or what I might try to fix it?