Could be the brake master cylinder pushrod squeaking, or an internal diaphragm in the booster squeaking. You can try to lube the rod to see if that helps. Many times I have experienced this noise - only sometimes have I experienced it solved.
Your answer seems to be most correct. This car has a lot of other components attached to or close to the brake pedal; thereby making the "lubricating" project difficult, but not impossible. Also it "adjusts" brake pedal height to compensate for driver's foot reach. I am wondering if the booster and/or the master cylinder might need to be replaced. Sounds expensive. What's your take??? Thanks.
Most of the shaft is concealed, so even if you can get under there, it's hard to lube. Don't focus on the adjustable pedal portion - it's not your problem. You COULD replace the booster and or master for the problem, but for only a noise, I'd personally live with the noise. Your new one could make noise too (early on or after a bit), adding insult to injury!
Dave, your response is right-on. I was told the O-Ring in the booster (where the push-pin rides) gets dry, and lubricating it will be a temporary answer. It will solve the problem for a while. It's worth a try. Thanks.