Partly an echo of the spoken word can be heard
The so-called acoustic feedback is one of the most tiresome and oldest problems in audio technology. It can happen that the microphones of some headsets cause feedback when they are too close together. Check the settings of your smartphone to see if noise reduction is activated. This feedback can also occur when the network is too weak. Sometimes it helps to turn down the volume a bit.
Ideally, all tour participants should use a headset (preferably a noise-canceling headset) and not stand too close together.