Genz Benz Shuttle 6.0 2x10 Buzzing!!

[Pauly Mob]

Can anyone help?? Here goes, My Genz Benz Shuttle 6.0 2x10 has developed a buzzing noise but only when I turn the volume up on the guitars:confused. While she's idle she's silent, Just the hiss from the horns. I use a 4x10 EDEN NEMESIS extension cab. I've had the amp tested came back clean, I've had both my P Bass and my Hagstrum 8 string checked for bad earth, came back clean. I've changed all power, instrument and speaker cables still buzzes. I am now at a loss. The 2x10 and head are only 7 months old. Anything I need to be looking for?? Anything I've missed?? Yours hopefully Pauly

[agedhorse]

Does the nboise increase and decrease with the volume control on the amp?

How about with the volume control on the bass itself?

Have you checked that you have a properly grounfded (earthed) power source?

Where are you located?