What can be done in the settings of the TSA-a/b if there are whistles and/or choppy voice transmission in the door intercom?

Both phenomena occur if the gain of microphone and loudspeaker together is too high and/or (with 2-wire door stations) the adjusted impedance is not correct. First change the set impedance (600 Ohm or Zr) and see if you get an improvement. If not, you must reduce the gain.