It sounds like mains hum. It's interesting it doesn't go away when they were powered by a bench supply. The only other thing you could try is powering them off a battery. Note if you try this with a large lead acid battery, such as a car battery, then it must be protected by a 10A or lower rating fuse. If that doesn't work then I don't know what else to suggest.
I've heard some bad things about Bose on the Internet, regarding the general build quality and people often claim they sound inferior, yet someone I work with thinks they're great. I don't have an opinion, other than Bose are unlikely to be better or any worse than other consumer audio equipment, possibly just more expensive, due to the branding.