<<We arrived today, back home, again in a 320. That noise is just annoying. Again there was a strange situation right after the plane landed (so we dont worry that much anymore) where you can heard the "wwwooof, wooof, wooof, wooof" of the PTU (as i learned here) but easily 1 minute after the plane touched the ground all the way to when the pilot shut the engines off there was a screeching "weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeee eeeeee" and it never stoped until we were in the gate and the barking sound started to come on and the screeching sound stoped >>
Probably the yellow hydraulic electric pump being turned on prior to switching off engine 2 for single engine taxi. The yellow electric pump makes that noise. The PTU can operate when you pull in the flaps/slats at the end of the landing roll and can also be triggered during single engine taxi fairly randomly if ECAM can be believed.