It is somewhere between extremely improbable and absolutely impossible.
Even if we assume that a "leak" could pop up somehow at 133.8 MHz, we have to do with 3V (?) circuits using digital technique.
I think no explanation could be found in interfering (as in "blocking out") with the plenty of microVolts received from the ATC signal and the detection by an AM receiver.
A leak would be "heard" as noise and be in the tenths of microWatt level, only detectable by lab equipment with a physical (or very near-) connection to the culprit.