The 30a makes sounds that he should not, which was to the effect better 20a.

The amplifier module is buzzing once the BetaSub30a turn on automatically (from red to green light). It corresponds to a typical transformer hum, which consists of 0.5 meters it very clear from 1 meter still good, but unfortunately also more than 2 meters can still be perceived. I had previously the Betasub 20, which so fascinated me that I wanted to have more depth to 30a yet. And indeed, the 30a has an even cleaner and deeper bass response than the 20a, which is more than all right.
But one speaker cabinet (30a) of this type of currently 250-300 should not do by itself sounds that mingle with very soft music and quiet movie scenes.

Secondly, I would like to mention the "Bloppen" or "Plobben" here. This always occurs when the amplifier from standby (red LED) On (green LED) switches. In addition, it is available even during operation (permanent green LED). And whenever I press the Soundcloud- or YouTube Stream on my smartphone "Play" or "Pause". I close instead fine-resolution monitor InEars (headphones), then the Plobben is gone. It is 100% on BetaSub30a itself.

I think this transformer hum most people can cope with loose or overhear. In the Bloppen and Plobben but I'm not so sure, because there is always a small "rum". This rum gives an idea which has impressive potential of this sub.
Is rated Without his little noises of 30a from my point of view and for me perfect audiophile woofer what !, Design, shape and size, type or principle, as far as value for the adjustment and connection possibilities! Whether music or film.

That reminds me but a transformer hum is not noticed when "Betasub 20a" and a Plobben and Bloppen was only subtly, the 20a is for me unfortunately the better choice and more potent 30a goes back to Amazon.