Lux flight controller
Emax RS2205 2300kv
Little Bee 30a
Betaflight 2.4.0 (same issue with 2.3.5, and with CleanFlight 1.11.0)
UPDATE: This issue was solved by RCGroups forums member quad007. Vibrations were getting to the flight controller from the frame via the nylon screws and standoffs and causing feedback issues. It was fixed by isolating the flight controller from the high frequency vibrations. The post is here:
http://www.rcgroups.com/forums/showpost.php?p=34044934&postcount=1639