While in Cruise Control, Dynamic (Radar) at about 70 mph, for no apparent reason a chime will ring 4 or 5 times and the car will slow down dramatically (brakes) to about 60 mph, only to aggressively speed back up to 70.
It may repeat this several times until I just hold the accelerator to hold speed.
Weather, sunny and dry.
Traffic, often NONE!
Sporadic. it may go months without a re-occurrance.