What's needed is a Ground Loop Isolator.
Here's one from PAC:
http://preview.tinyurl.com/PACGLI (Amazon.com)
Here's one from Kensington:
http://preview.tinyurl.com/KensingtonGLI (Amazon.com)
I'll let you all know how the Kensington works out after mine shows up tomorrow.
Ooohh! Now that's what I'm talking about!
Looking forward to hearing how that works out!
Thanks! (yippy)(cool)
Works awesome! No more interference and (importantly) no degradation of audio either! (cabpatch)
One beef with it, tho'... the "nodule" that constitutes the filter is ~1/3 the way from the end with the narrow jack housing. Not a problem connecting my iTouch to the wide jack with the dock cable, however (about 1mm between them); dunno whether it would be problematic for an iPhone.