Hi, I seek your help/advise as I am stuck in a classical situation. "It worked fine so far but today when I need it ..." My setup. : Recording path: Mics >> Mackie 1640 >> Firewire >> HP NX 7400 Laptop Monitoring path: Mics >> Mackie 1640 >> Aux 1, 2, 3, 4 >> 4 channel headphone amp. What happens: All connected as above, the laptop runs on batteries there is no issue. Jittery noise comes up as soon as I connect power supply to the laptop. If I power up the mixing desk (connected via firewire with a laptop) the noise becomes even louder. Interestingly the noise is loud even with the volume knob all the way down on the headphone amplifier... Tried: Tried various electrical sockets. Connected both laptop, mixer and headphone amp to the same switch board and then to 3 different sockets via extension leads. Tried different cables. No luck. Anyone has any idea what is going on and how to sort this out?