Originally Posted by tastycaramel
What's that for?
TWARE called a ground loop isolater. That is probably the best term to use. The hum/buzz appears to be electrical interference between the phone's charging port and the headphone jack. Putting the ground loop isolator in the middle filters out the extra noise. It works really well and I picked mine up for about $6. They wanted $20 at Radio Shack so it pays to go online.