Sudden buzz in the sound, i may need some advice please

[chapelier fou]

Hello

i got a sudden persistant buzz in the sound, low pitched, but only when i power my edirol pcr keyboard via USB (which i've been doing for years). if i use the power supply, no noise.

i changed the FW cable of my soundcard, same thing.
i tried another soundcard, FW powered, same thing.
i tried pluging the keyboard in the other usb slot, same thing.
i tried pluging the keyboard in a powered usb hub, same thing.

i want to come to the conclusion that it's not the computer, but the usb power system of the PCR keyboard which has a problem.

Am i right ?
Could i have forgotten something ?

Thank you for your help !

[Warrior Bob]

Is that sound coming out of your computer speakers or out of something else, such as the Edirol keyboard?

[chapelier fou]

Ha !
in the speakers !