I don't have any info for the '99 but these are the wiring diagrams and module location for the '97 - it says the module is on the rear of the interior fuse panel. The wiring diagram states that the chime will sound when the driver's door is opened, but elsewhere in the manual it states that the chime will sound in response to either front door opening. I would suspect a bad contact in the driver's door courtesy lamp switch rather than a failure at the module, so I'd check out the switch first.
'97 Escort warning chime wiring diagram - part 1
'97 Escort warning chime wiring diagram - part 2
'97 Escort warning chime module location