I have to confess I haven't done a visual inspection as yet. UCA boots were cut/torn slightly when I purchased 14 months ago. I have 034 AUCAs on my bench to install, was waiting to put them on with PSS9s. Now may be the time. Chatter gets worse as car gets warmer, because I have a Cabrio, the sound transmits right up the reinforced A pillar to into the cabin, making it sound like it is internal, but there are no parts in the pillar that I am aware of that could be source of chirping squeak.
I think it could be UCA ball joints, or perhaps upper strut mount. Any other possible causes to look for when I pull the wheel this evening? I am hoping it is time to order the PSS9s and just refresh the whole setup. 103K on the car, probably 60K on the stock suspension (PO had Vogtland coils on it for a while before returning to stock to sell on to me.)