Bit of an off-beat question this, but I'm trying to get a sound system set up in one of the Bermondsey arches (just a simple amp and mic thing is the order of the day) but the sound set up we currently have suffers from random bursts of electrostatic noise from the railway above. Would anyone be able to suggest a way of immunising the kit we have or know what sort of frequencies we should avoid if we go down the route of selecting new gear?