I have a 2005, 4.6 L, STX model. When the blower is turned on, about once or twice a minute you will hear a switch-like sound. Similiar to something switching open or closed. I turn the blower off and the sound goes away. Everything works fine. Anyone ever has this or have any idea what it might be?

 

Sounds like either the blower motor is going out or the blower motor resistor is going bad...

 

It could be the blend door for defrost getting snagged.
If it was a resistor pack you would probably have issues with certain blower speeds not working with the AC on.