Why do GSM phones make noise when making calls or receiving text messages near the speaker, but CDMA phones don't?

Not because of radiation or signals, but because of principle.

GSM network uses waveform signal protocol, which will interfere with the waveform model of audio.

While CDMA uses 0. 1 binary, so it will not be disturbed by the outside world.

In other words, GSM network can be shielded by jammers, shielding the bad information in the examination room, while CDMA is not disturbed.