Speedbrakes extend sound bucle landing

Hi again!still configurating to get 100% the 737,but testing landings,with Flaps 40 and Bugs set,speedbrakes armed,when touchdown all works OK,reverses unlocked,speedbrakes extended but i dont know why i get a bucle sound of spoilers lever again and again and again until i set a little bitof throttle bit to get off reversers and spoilers.

Why the speedbrakes lever extend sound comes in a bucle?.

Alex