One of my 41's doesn't like modules in port 4

[damaltor]

(Old title: One of my 41's doesn't like its card reader)

Hi everybody,

i have one HP41C, tall keys, which doesnt like the card reader. If i plug it in, even before switching the calculator back on, the calculator makes a very silent noise (sounds like an inductor singing the song of a short circuit). After removing the card reader, the sound is still audible. If i switch the calc on now, it shows random patterns on the display, until i remove the battery and wait a while. No other way to bring it back as far as i can tell.

The calculator works fine, i tested the slot with a quad memory module (which also works fine) and the card reader works well with a different 41, even when i use the exact same battery. Any ideas?