HUMM from subamp - only when Laptop plugged in...

[JRace]

I am using a class D BK1000 amplifier to drive a tube shiva sub.

I have a lptop in my audio chain and whenever it is plugged into AC there is a very audible anoying HUMMMM from the sub amp.

The sound goes away only if I do one of the following:
Disconect the AC power to the laptop,
or
Disconect the vga out from either the projector end or the laptop end.

Any ideas?

The hum is present even without CATV connected.

My signal chain is:

Laptop:
- VGA to projector
- Optical SPDIF to receiver (tried onboard optical SPDIF, onboard analog , outboard usb optical and coax)

Receiver out o sub:
- LFE/Sub 100Hz to BK1000 subwoofer amplifier via analog RCA

Thanks for any help....

[JRace]

Update:

The unwanted HUM is gone when I remove the 35' DVI-HDMI cable from the signal chain (either at the DVD or the Proj).

When I turn off the laptop screen the HUM is gone.

When I reduce the brightness the hum is worse....

Seems like noise is being introduced with the laptop that is coming back through the DVI and into the sub amp....

[Original Burnedfingers]

Disconect the AC power to the laptop,

This is a common problem. Try making sure that the lap top and the projector and any other items do no share the same circuit.
Try a cheater 3 to 2 plug on the lap top.

[penguinpaul]

It's called a hum loop. Simple fix - You are probably using an extension lead/plug block?. If so, don't. Plug them into a different plug socket and the problem should just vanish. I think it's sometihng to do with earthing...