Then I would have a global variable, something like "whichsound" if whichsound = 0 you play sound 0, and switch variable to 1, so next time event is triggered it plays sound 1 and switches back to 0. Sounds will alternate and you only need a single trigger.
In my sample you have a variable ( call it triggersound or whatever ) that's reduced by 1 each tick, from 60 to 0. When it reaches 0 event is triggered and variable reset to 60 to start the countdown again . Now 60 is the starting value stored in a variable called stress. You simply set this to stress = 30 and sound will be triggered twice as fast, you can set it to anything to speed up or slow down triggering. That stress variable can be set by anything you want ( in my sample by position of the square you drag ).
To simplify ( hopefully )
soundvar = 0
rate = 60
triggerspeed = rate
System Every Tick > subtract 1 from triggerspeed
if triggerspeed = 0 trigger sound ( 0 or 1 )
If sound 0 played, set soundvar to 1 so next time it plays sound 1 ( and the other way around )
set triggerspeed back to rate
Changing rate variable will speed up or slow down triggering of sounds
I am sure there are other ways to do it, but I am used to using timers like this.