There was an AU-10 and AU-20. Believe the -20 fixed this problem and by now all have likely been modified, but...
While the unmodified AU-10 will work fine in a glass panel, using it in a metal panel will cause an electrical ground loop (two different paths to ground).
You may notice the vario deflecting when the radio transmits. If that happens, look at the ground trace near the mounts for the AU circuit board to see where to cut.
Just remembered a head-scratcher from 32 years ago?
Jim