There's always a little break between loops. It's small but noticeable. Is there a way to get rid of the break?

You should not loop whith a forever block instead of ‘play sound until done’ block try start sound block and play the the sound and count how many seconds the song or sound effect is so
Place a block called start sound in the coding compartment and take a wait block and put in how many seconds you sound was
Then do this over and over until you have a loop!!

another option is to use the forever and play until done, but cut out the ending of the song in the sounds editor

Vibrato wrote:

another option is to use the forever and play until done, but cut out the ending of the song in the sounds editor

forever
play sound [loop v] until done
end

This is the block he is saying, and you should check the sound file first, I made a project to demonstrate it in case you still find it confusing:
https://scratch.mit.edu/projects/419547344/
You should probably either use play sound until down if you have only one loop sound, but for more than one you need to use the timer block to avoid lag ruining your transition