997.2 GT3 tick at idle

[mm450exc]

First thought it's the vacuum pump but can't hear the noise coming from it. Unable to track it really.

Symptoms:
1. Only can here the ticking noise inside the cabin
2. Starts about 2 minutes after cold start
3. Comes and goes. Can increase in frequency at same rpm.
4. Blip the throttle to 3k rpm and it goes away. Then comes back.
5. Only get the tick at idle
6. Not constant. Comes and goes.