I am happy to report that I managed to eliminate all hum and buzz from my LP playback system. The solution was simple: I connected a wire from the ground connector of my LP player to the ground connector of my Reflex preamplifier. When there is no signal (meaning when no LP is playing and the amplifier input is selected to which the Reflex is connected), even with the volume control of the amplifier at the 12 o'clock position, all I hear is a gentle quiet hiss. No more hum or buzz. I should have done this much earlier. All this time I thought the hum came from my amplifier or the electrical system.

So is there any way of also reducing or maybe even completely eliminating the hiss?