Loops of fury?

i’ve made an animation, and after the previos 2 scenes have finished, i have a vibration effect on the 3rd scene that i want to be continuous, how do i tell the animation to just keep looping the third scene after the previous 2? i don;t want it to go back to the beginning after scene 3, i want it to go back to scene 3 (beginning of)

any help is greatly appreciated