AFAIK the magnets are mounted on spinning discs, the sound is the motors driving these discs.
Yes you are correct on this one. I'm almost certain that the 'hoverboard' is simply made using a collection of 4 halbach arrays (basically a smart arrangement of magnets to increase the field on one side) mounted on spinning disks spinning like a quadrotor to cancel torques. The sound is made from these motors spinning at high speed. Directionality can be controlled like a quadrotor, by spinning some motors faster than the other. Therefore, no expensive semiconductors for high power switching (which I believe is what most people think, i.e. using an electromagnet). This is not a particularly novel method though, and has been done by many people (a search on youtube should give lots of videos over the past few years).
What I think most people are not aware of is how dangerous this can be considering the large number of strong magnets at the bottom of the Hendo board. For example, any small magnetic object would get attracted to the bottom of the board immediately. If this object is larger than the 'hovering' distance, it could seriously rip up the bottom of the magnets. In addition, putting this anywhere near any magnetic surface would cause it to stick, making it almost impossible to remove safety, and crushing any fingers that got in-between during the process. Not to mention all the other impracticalities like transporting a really strong magnet around, and the extreme cost of a copper floor (this would work on aluminium as well, but the motors need to spin significantly faster since it has about 50% higher electrical resistance.
I always thought this would be some sort of fun physics demonstration most EE engineers played with before though, like spinning a magnet or a conductive disk and making it levitate a magnet / disk, and I encourage you all to have a go playing with a setup like this. However, the reasons why this product (a hoverboard made using this method) has not been made a long time ago are due to these inherent and obvious dangers.