helto: Actually, add a "System: Trigger once" condition to the "Mouse: Over object" event.
The problem here has not to see with the Audio object, but with how events work.
Every tick that a condition is true, it executes the actions.
So every tick that your mouse is over an object, the Audio object plays a sound.
The system condition "Trigger once" allows that the actions are only executed once while the conditions of the event are true, so it plays the sound only one time.
Edit: the condition to check if an animation is playing also does the trick for the same reasons.