Autothrottle Retard
In 1986 I was involved with a situation at a small airline with 747-200 who had a rash of autothrottle retards at about 250 feet on approach. Turns out the radio altimeters were spiking down to 0 feet at that point, causing the A/T retard. Pilots reported it was subtle enough that it could have been overlooked long enough to cause grief.
GB