Don,
Laptop humm often comes from their lousy power supplies, a problem that is easily solved by installing a three prong to two-prong adapter to the laptop's AC power supply plug. It works for me!
Good Luck,
Gary
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Travlin' Easy
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)