How to make backgroud music: I have some difficults in background music or noise,such as jittered timing and defferent volume

I need white nosie as background music , so I set sound component in each routine.
However, the white noise didn’t play continously between routines and when my feedback ton played each trial the volume of the white background noise decreased.
Except that when the background music in a trail is not long enough ,there is no sound anymore,how to make the noise or musci automaticly play again?

I’m hoping someone can help me find the way to solve these in builder.Or do I need another player to handle this?
Thanks in advance!