Good call...
Relief that your rig is fine.
Your PC interface should not introduce that much noise into the rig. The fact that it is tells us that something is terribly wrong. My initial thought is that a ground loop has been formed.
Can you tell us more about the sound card interface you are using?
I am not using the pc as a audio device, because I cant get Line in to work and that's typical of Dell and there built in SigmaTel audio sound cards.
I recently sold an 11z Dell to a friend. He's having same sound card issue problems.
Okay just tryied it with headphones and it sounds much worse and it seems 20m shows the worse clipping. I also tried it on a battery and it still does it so I dont know what is up.
is your interface homebrew or commercial ?
Here is the Icom cable and, USB extension cable currently choked.
Who cares about the usb cable being choked. that bad boy needs to be choked right at the 1/8 in ci-v jack.. on my home brew interface i used a RadioShack® 100 µH RF Choke | Catalog #: 273-102 at the pc board.
but on your setup i would try on of these.. Snap Choke Core | Catalog #: 273-067
Or Catalog #: 273-105
and get as many wraps as close to the 1/8 inch jack as you can.
Your problem isn't the usb side of the interface it is the serial side that connects to the radio. when the radio sends or receives data there are small voltage spikes and that is where you are getting your noise. If you cut your cable and put an led across the wires (with a resistor of course) you would see the activity.