I have developed a loud buzzing noise withe radio still working this is intermittent and occurs with the radio and cassette player it is a Philips R750(Rover Car)
Does the buzzing occur just before you recieve a text message or phone call on you mobile phone (most likely times but sometimes it can occur when the phone is registering to the network). If this is the case then simply move the phone further away from the radio and the buzzing should disappear. Hope this helps.