playsound command for a jetpack

You probably want to loop the command slower. You can do this using redstone (just a regular redstone clock).

If you don't want to use redstone, you can tell the command block to only execute the command every few iterations.
To do this, you assign a timer scoreboard to the player that ticks up every game tick and only if it reaches the time you want, the sound gets played and then the timer gets reset.

Setup:

scoreboard objectives add timer dummy

In loop, replace @p with the selector of the flying player and ... with the rest of your playsound command:

scoreboard players add @p timer 1
playsound @p[scores={timer=20}] <...>
scoreboard players set @p[scores={timer=20}] timer 0

If it's a function, you can also use /schedule (archive):

/schedule function <function> 20

or:

/schedule function <function> 1s