I’m checking out the audio decoding capabilities of the Pioneer BDP-LX70A Blu-ray player and the Yamaha RX-V1800 home theatre receiver. To help me I have Dolby Laboratories’ Blu-ray demo disc, ‘The Sounds of High Definition’. After I had done my checks, using specific tracks, I just left it running while I was writing something. After a while I 
noticed a series of powerful thumps that didn’t seem to relate to the music (a bit of light Mozart) that was playing. This was during selection 3 of the Dolby Digital Plus demo material, entitled ‘Elements: Air, Earth, Snow, Water’. It was at the start of the ‘Snow’ section (about 1:20 into this selection).
I went closer and had a look at the subwoofer I am using this week, the REL R-305, which didn’t have its grille on. The driver was pushing huge amounts of air, visibly displacing by a centimetre or so, and then tailing off slowly. The sub happened to be plugged into my power meter, which was flicking to 50 or 60 watts during these pulses. So of course I measured the LFE signal by plugging the receiver’s LFE output into my computer.
The top part of the graphic shows all nine of the pulses, while the bottom part zooms in on the third pulse. Fundamental frequency: 11.7 hertz!
Why is this there? Is it a ‘heart beat’? Or a mistake?