Noise on radio - help !

[Buckingham]

I've got a UHF Puxing 777 connected via Autocom, which works very well bike to bike, except that I keep receiving bursts of noise, typically lasting for 10 to 30 secs. The radio must be receiving something !
There are quite a few settings on these radios - is there anything I should try ? All I've done so far is to set the channels to UK PMR446 frequencies.

Thanks