Flutter is oscillations increasing in amplitude until structural failure occurs, so no flutter.
Reversal is when the flight control surfaces move the stick instead of stick moving the flight controls. Will only happen in aircraft with unpowered flight control surfaces. In a Learjet you could experience reversal in the form of aileron buzz at Mach above Mmo, progressing to mild aileron snatch due to shock wave moving aft and outboard on the wing, impacting the ailerons. But not at 300 KIAS low level, and certainly not in a Boeing 737.
What you probably have experienced is the increased roll rate which Boeing mentions in the very early FCTM:
Deploying speedbrakes when initiating a turn can cause a more rapid roll rate, which the A/P then will try to compensate for, thus the oscillations. You are working George too hard, and he is trying to tell you something!
Or maybe its just the guy next to you getting shaky because of your energy managment
