How to Eliminate the Hum From a Computer Audio Output
Step 1: Determine the source of the hum by eliminating possibilities. Check all the connections between the speakers and the computer. A poor connection can introduce a ground loop and humming.
Step 2: Wiggle the speaker cables to see if the hum is intermittent or consistent. An intermittent hum may be caused by cracked or broken speaker wire.
Step 3: Ensure the computer is plugged in to a grounded outlet. The three-pronged plug has positive, negative and grounded terminals. Without the ground a ground loop can be introduced into the audio system and cause a hum at the frequency of the alternating current. Computer speakers can add extra, unwanted noise picked up from other electrical signals.
Step 4: Move or remove any radio frequency transmitters close to the speakers. Wi-Fi routers, cell phones, microwaves and baby monitors are all RF signal generators that can cause interference in poorly shielded audio cables, which is interpreted as a humming sound.
Step 5: Add ferrite beads to the speaker cable to block any RF signals that cannot be removed. Higher quality cables often have the electromagnetic shielding material built in, but you can purchase snap-on ferrite beads for unshielded cables. Typically you want to snap the beads close to one end, the other end or both.
by James T Wood, Demand Media