weird tick tocking sound in passenger dash

[GPReyes]

past two days I've had this tick tocking sound (like a horse trotting) comin from the passenger dash area (like under the airbag)

it starts when i one click ignition and and continues when i start the car.. it;s quite audible and then disappears when i turn the a/c on...

so obviously it must be an a/c problem? so far no probs with airconditioning or temp or car performance...just that annoying sound ...

anyone know what it is?


GP

ps

car is a 2000 boxster s tip

many thanks!