I'd have to agree with you there. In one of our projects we had an audio amplifier IC that when powered would emit a terrible GSM buzz whenever a transmitting phone was within 6 feet of the PCB. But we redesigned it to use a more noise immune amp and now do not exprience the problem.

It has a lot to do with the topology of the amplifer as well as the signal routing. A differential signal all the way to the transistors, fets, ICs etc will help immensely. In our case we are using a 1 watt digital amplifer with single-ended connection but were using a BTL (bridge tied load) device.

Stu