why does the truck make a constant tick for a few minutes when turning on/off? on 1994 Chevrolet 1500 Pickup

when the key is turned on and off, a tick comes from the area under the dash on the passenger side. it lasts for about 2 minutes and then shuts off. it also ticks whenever you turn the a/c or heat on for the same amount of time. it does not affect the drive of the truck but is annoying and embarrassing.

Asked by for the 1994 Chevrolet 1500 Pickup
My truck also 94 chevy does same thing, co-workers said it was a chevy anti-theft device to make thieves think it had a timer for a bomb, they bought toyota trucks- don't do such silly things.