does it come back by just touching the volume control knob, if it has one on the set itself, if so it could a build up of (for want of a better word)dirt in the control, with the tv off wind the knob back and forth fully a few times this should clear it ,but only temporary,if its only doing it by the remote control volume buttons then i can't help you
Either because theres a lot watching draining the transmitter or your meter is ready for another shilling,
Seriously though, maybe its time to think about one of them new coloured ones, they say Dixon of dock green looks great coloured.Get some brass spent,dont bother about licence,switch off and hide in cellar if someone knocks.Weve got away with it since the coronation.