呢個係咩現象?

It is interference of electromagnetic signal.

When there is incoming/outgoing call, the mobile phone will emit strong 900MHz RF signal. Closer to the mobile phone stronger the signal.

In the PC speaker, there is a amplifier circuit which amplify audio signal (small voltage ac signal) and drive the speaker units.

The RF signal can easily jam into amplifier circuit.

Good quality speaker doesn't has such problem.

may the frequency of the speaker similar to the frequency of the mobile phone?

我都試過咁
我認為是(復射)or電磁波等等的問題