DIAGNOSIS Electrical interference on the power line or a ground loop. The Beam's amp is sensitive to dirty power or interference from other devices on the same circuit.
FIX Plug the Beam directly into a wall outlet, not a power strip, surge protector, or an outlet shared with other high-draw devices like a mini-fridge, fan, or fluorescent light. If it's already in the wall, try a different outlet on a different circuit.
IF THAT DIDN'T WORK The issue could be a ground loop introduced through the HDMI cable. Try a different, shorter, high-quality HDMI cable. If you're using the optical adapter, ensure it's firmly seated and try a different optical cable.
HEADS UP If the popping coincides with your thermostat kicking on or your fridge cycling, it's definitely power interference. A quality power conditioner can help, but that's a more expensive fix. First, just try isolating the Beam's power.