Why did speakers used to make a strange noise when a phone is about to receive a message? Also, why that doesn’t happen as often now (little to no instances)?
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It wasn’t the speakers themselves, but rather the amplifier. First of all, back then the frequency phones used to operate at was different (900MHz) and fixed. That particular signal would interfere with the audio signal the amplifier was, well, amplifying.
Your phone is not constantly emitting a signal. That would drain the battery and keep the bandwidths busy. Instead, once it’s registered with a tower, it stays put until that tower emits a signal seeking your phone. So whenever a text message would be received, your phone would “wake up” and confirm its presence to the network in order to receive the message. Also, the interference was also present during calls, but the text message had a specific pattern. If you held your phone next to an amplifier during a call, you’d hear a constant sound.
Nowadays, phones operate on a multitude of bandwidths. Furthermore, newer audio equipment is shielded against intereference, as older equipment was designed before mobile phones were as popular.
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