The only thing I can think of is that your keyboard wasn't grounded at the power source.
Or, an unshielded cable was near a transformer or something.
Have you recorded on other disks since your upgrade? Is this the only disk that makes the hum?
Did you upgrade your sound card drivers? When you say "Up graded your computer", do you mean software or hardware?
Did your friend pop the hood on your computer box? If so, open your computer and check the cables to your floppy drive.
If your disks play ok when there is no keyboard being played, I'd say to begin with the keyboard.
Check the receptical it is pluged into for proper ground. Maybe your dad has a ground checker you can use.
Check the plug in cable connections from your keyboard for crud or that green stuff that builds up on some during the wet season.
Check your keyboard cables for a bad kink that may have a broken wire.
Repost and let us know. If none of these ideas help, someone will come along with more.
Good luck.
