Pulled head stud would make a more aggressive sound, I think (And hope) and would be there all the time?
I have the same chirp on and off; I removed the belt to feel the alternator bearings: They feel fine, alternator spins freely.
Distributor is oiled religiously, so, ?????????
I'll try the soap trick when it comes back and would be very happy if that is the problem.

I had a similar sound in an 88 3.2 liter that I bought a few years ago. Mine was more "squeak" than "chirp" though.

It took me several weeks to discover a family of mice had made themselves at home in the space immediately behind the ignition key. It's a perfect little space for these critters - with lots of little cables to chew on.

I had the same thing happen years ago with a VW - carbureted of course. The chirping sound was sort of syncronized with the engine turning over. Drove me nuts. What I finally found out was that it was sucking air in at the base of a loose intake manifold. When I tightened the nut up where it was sucking in air, the chirping stopped. Check it out before you burn a valve.

Heater fan motor, take the motor connection off...even in summer, this motor comes on to cool the heat exchangers when the engine bay gets too hot.

Mine did it, take it out dissasemble it, lub the shaft if not too gone...there are 2 screws holding the motor together, 2 tabs on the side have threads. Once the screws are turned out, the tabs slide out of their slots allowing the rotor shaft to pull out of the case.

I'm amazed that so many other owners have this problem. I have ruled out "oiling the distributor" - opened up my distributor and there was no felt thingy. Spoke to my mechanic and he told me the later 911s (mine is a 1988 model) don't have it and doesn't need it (I can't remember why). Am going to try out the soap route next.

I have a chirp or as I call them crickets, but I have the bearings and belts replaced and still getting a noise from the bottom of the engine on the drivers side. Two different mechanics said it is coming from inside the engine and both think it is the hydraulic lifters. I am hoping they are wrong, I am taking it to another mechanic this week. In my case it is loudest at idle usually when I first start it up and quiets down while driving. If I push the RPM's and get it warmed up a bit the sound will go away for a bit even at idle (stopped.) I guess it has to do with oil pressure and temperature in my case. BTW, I have a 1999 911 C2. If anyone has any ideas about my situation, they will be greatly appreciated.

Thanks