I recently purchased two sets of SHD8600 headphones. They both work well individually connected to the headphone socket of my TV set. When they are both connected (using an RCA double adaptor) and in use at the same time, one or the other of them cuts out intermittently (approx once every 10 minutes). Sometimes they both work OK for up to 30 minutes before one gives up. I then can't switch off the non-operating headphones without removing the batteries (or waiting for 5-10 minutes for them to switch off themselves). Any suggestions? Is one headphone set faulty?