PT Cruiser - door locks

We own a red 2002 PT Cruiser Limited Sport Wagon 4D. It has just under 100,000 miles on it. We bought it in 2004, in San Diego. Almost immediately, a peculiar problem began to manifest itself.

When the weather is warm, above 80 degrees, and especially when it is damp ? either raining or very humid ? the electrical door lock system goes nuts. The doors lock and unlock themselves intermittently, and we hear clicking sounds even if the door locks do not engage/disengage. Sometimes the interior lights go on. It happens when the car is moving or sitting still with the engine running or with the key in the accessory position.

Can anyone offer any ideas about what causes this or what we might do? So far it is an annoyance rather than a serious problem. But it is a little creepy to be sitting in a stationary car and have the doors lock and unlock themselves. Thanks in advance for any help you can offer.