Europa-List: radio

[Paul Stewart <europa@pstewart.f2s.com>]

I've done something stupid but can't work out what. I have a microair  
760 radio wired through an XCOM intercom. Fired it all up for the  
first time this evening. To my great surprise it all worked (almost).  
Radio receives fine. Intercom works a treat. Even the music input  
works. However when I press the PTT (either P1 or P2) a get a loud  
buzzing in the headphones - the radio also transmits this buzzing. It  
does this even without a mic plugged in. Anyone suggest what I've done?

Regards

Paul
G-GIDY