Puzzler: 10db hum via USB audio box on MacBook Air but not iMac

[Butterking]

Hi any and all. Hoping someone in the community can help me figure out a problem I'm having.

I have Furtech GT40 24/96 USB DAC, which I really recommend for things like ripping vinyl. Its like three boxes in one.

But I have a problem.

I have a brand new Macbook Air and when I connect the GT 40 to the Air and attempt to record using Audacity or Adobe Audition (beta) I get a 10db hum in only the right channel. Weird thing is, I get the hum the moment I connect, so even if there is no analog input or output connected to the GT 40, only the USB between the Air and the unit, when I start to monitor in the recording program I see the steady hum. And when I record, it is there in the background.

The same GT40 unit hooked up identically to my one year old iMac at home has no hum whatsoever. It is rock solid quiet.

What is it about the Air that would cause this problem? I thought for days something was wrong with the GT40 until I hooked it up to troubleshoot and realized it works perfectly on the bigger computer.

Thanks in advance if you can offer any theories.

Erik

 

[paolo-]

What plug to you have on the end of the air? If you're not using the 3 prong one, you're not grounded. That might be the source of your noice, if the usb box is usb powered.

 

[Butterking]

What plug to you have on the end of the air? If you're not using the 3 prong one, you're not grounded. That might be the source of your noice, if the usb box is usb powered.

What's truly bizarre is I get this whether or not the Air is plugged into AC or running on battery so it isn't about a grounded plug.