My new amplifier came with 4 SED Winged C EL34, biased at 30mA by the seller, to extend tube life, 40mA is recommended by the manufacturer... Sunday I changed bias to 40mA, when I switched off the amplifier, the speakers made a loud noise, same noise Monday... :eek: So today I changed back to 30mA, switched off, no more strange noises... I saw people recommending 50mA, saying it sounds better... What could be the problem, tubes or amplifier... :rolleyes: