Alright so, put back that trigger once at the bottom...
I tested here, and it works fine to me...
I created two events (one handling the animations with the mouse, making the run animation play only when left mouse is down), and another to handle the footsteps... like this:
Mouse | Left Button is down | Set Sprite Animation to Run
System | Else | Set Sprite Animation to Stand
Sprite | Is Animation "Run" playing | Play Coin not looping at volume 0 db (tag "")
Sprite | Animation frame = 1
System | Trigger Once
Here is a capx:
https://www.dropbox.com/s/mf8d3bub61kv5 ... .capx?dl=0