Oh dear, If its always the same time, I suggest throw a big down pillow over the phone to muffle the sound.

One of my geeky friend have recorded the distinct sound when the phone company tells you that the phone is no longer in service. And its the first thing the answering machine plays. He says he doesn't get any robo calls or unsolicited annoying calls. Works like a charm he says.

I think the school robo call system will recognize and remove you from the list automatically.

If you need that .wav file, I can ask my friend for it. and send it to you. then you can play it on your computer when you create your new outgoing answer message. \It has to be the first thing on the message.