If you try without air/paint and with the eyes off, can you get it to do the same thing? i.e. you pull the trigger, then 3 seconds later you hear the microswitch click? If so, sounds like either there's a problem with the switch or the alignment of the trigger.
If not, try it with just air and see if you can get it to occur. In that case it might be that the solenoid needs cleaning. When it happens also keep an eye on the pressure gauge and see if that's doing anything strange.