I´ve had similar disturbances in B757 at my home base where landing on a particular runway, the exit is a 90° turn off the runway in front of the LOC antenna, saw the preceeding (also 757) one day in CAVU wx and as he turned 90° on the end my LOC signal went full left, full right and back to middle. Happened too quickly for the A/P to do much except wiggle the wings, but in IMC approaching minima, definitely not what you want.