2001 Parking assist speaker

Where can I find the parking assist speaker for a 2001 Windstar? All sensors are clicking when in reverse so I think the sensors and module are good. Light is on in dash and no sound when standing behind van in reverse (parking brake engaged).

Thank you.

I found on another forum that the speaker is on the passenger side behind the D pillar. I think that is where the rear of the sliding door is.