Buzzing sound from U46mk2 when power pluggedin

I get a very loud buzzing noise when I plug in my mixvibes U46mk2 soundcard with the power plugged in. The buzzing stops if I:
- switch to battery
- unplug the external soundcard USB
I get no buzzing in my headphones: bear in mind I plug my headphones straight into the normal RCA output at the back of the sound card using an adaptor.
I have tried plugging my headphones into a different output, as well as plugging the master out into a different output,but this makes no difference- still buzzing over the mains, and no buzzing in the headphones.
I can only conclude that something relating to the ac power supply is interfering with the grounding of the sound card.
Please can someone recommend something.
Should I:
- buy a separate 5volt adaptor for the sound card?
- buy a new ac adaptor for my laptop?
Thanks!
- switch to battery
- unplug the external soundcard USB
I get no buzzing in my headphones: bear in mind I plug my headphones straight into the normal RCA output at the back of the sound card using an adaptor.
I have tried plugging my headphones into a different output, as well as plugging the master out into a different output,but this makes no difference- still buzzing over the mains, and no buzzing in the headphones.
I can only conclude that something relating to the ac power supply is interfering with the grounding of the sound card.
Please can someone recommend something.
Should I:
- buy a separate 5volt adaptor for the sound card?
- buy a new ac adaptor for my laptop?
Thanks!