Audio problems when using USB powered speakers

[andyz]

Z170-HD3P-CF (U3E1)

Hi all,

I'm experiencing problems when trying to use a pair of small USB powered speakers.
The audio is connected via the green minijack, with power supplied by a separate usb connection.

There's a low pitched howl/hum (sorry, it's hard to describe).
I've tried various audio configurations (2.0, 5.1, 7.1), disabling all other audio devices etc.
I've even take the speakers back and swapped them for a new pair, but still no luck.

It's not howlround/feedback as there's no microphone connected.

I'm suspecting some sort of shorting as they're fine if I use an external USB power supply - I'd stick with this but the whole point of buying USB powered speakers was to utilise a USB port rather than having to run mains and a converter.

Any suggestions gratefully received, thanks in advance.

[shadowsports]

Greetings,
Low pitched hum is often ground loop related.  Can have other causes however. 

Running out the door...  so tell us this.  Does your MB have an amplified sound chip or is it standard line level outs that require amplified speakers?  Are the speakers intended for PC or for a mobile device like a phone?   

Are you using a UPS?  Are you certain the power being supplied to the system is clean?  Have you tried with other speakers?