I had an issue that sounded just like this one and what I discovered was 
I had a ground loop problem between the equipment. The first this I 
would try is to reverse the plug on the power supply if the plug prongs 
let you. In my case I was able to plug in the laptop supply into the AC 
outlet strip that the amp was plug into and I solved my problem. . Your 
hum can be caused by many more things too.
Dennis Duke wrote:

> A friend of mine just purchased a new HP laptop for the express 
> purpose of playing music at square dances. We discovered that the 
> power supply is generating noise when he tries to play the music and 
> also when he tries to copy music from his record collection (old 
> 45's). What can be done other than running the laptop from its 
> batteries (which won't last long enough for and evening's music)? 
> There is no ferrite bead on the power supply lead. Would that help? 
> Any other ideas?

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No virus found in this outgoing message.
Checked by AVG. 
Version: 8.0.100 / Virus Database: 270.3.0/1505 - Release Date: 6/16/2008 7:20 AM

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