Cant find where function is being triggered

Hi guys,

This is a bit of a strange one because what i am trying to do seems to be already done in my project/fla.

On my website i have background images that get loaded randomly when every a user visits my site.
I was looking to making this a bit cooler with the background images continuing to change as the user browses the site.
Ok so here's the problem.

The function that i have in place at the moment seems to continually trigger and i have no idea why. I have it set to only trigger once when the site loads up.

Is there anyway to see where the trigger for the function is coming from?
I never have used the flash debugger and i am thinking that in here i might find where i will find where the trigger is coming from.

Can someone advise?

Thanks