New Proteus arrived. The audio seems to have background buzzing that is in synch with the frequency, going up and down in volume. Is this normal? I'd have thought I would get pure tones or beats, but this buzz/hum in the background is a bit of a surprise. Admitedly, I upgraded my headphones, opting for either heigh end cans or high end earphones for noisy environments. Is this just part of the package?