I have a strange configuration. I will try to describe it and why it's setup the way it is.
First, I run and host WebEx-style meetings for hours a day. My phone interface is an iPhone 4S since my landline does not do free toll calls, which drives most of my calls to my cell phone (unlimited minutes plan).
I have experimented with various BT headsets, but none seem to have the battery stamina to stay all day, and the quality of my voice going down the line is not always consistent, etc. The Apple wired earbuds don't have bg noise cancellation, so they pick up everything, like my keys on my keyboard, and the click of my mouse. Too sensitive...
Having some studio equipment around in not in use, I mounted an EV RE-20, mic mixer (with EQ, line outs, etc.) an iRig to convert line level back to the correct level for iPhone in, and of course, some nice headphones for my own listening to what's coming back up the phone line.
Obviously, running this from a cell phone drains the batteries of a cell phone, and that's where the noise issue comes in.
If I'm charging/powering the iPhone from the PC USB cable, I get what I can best describe as a high pitched crackling, almost like a modem sound, as background noise. It's not full volume, and it's not enough to make me pull my headphones out, but it is definitely there. If I power the phone from an AC adapter, not connected to the computer. The noise is not a hum like a 60hz ground loop would sound like.
I would like to connect my mixer to the audio in on the computer so that I can use the mic/mixer and other sources to do VOIP and such, but if this noise is present in the USB bus, I'm not sure how nice any of the other audio in the computer will sound. (BTW, Computer is a HP laptop, with docking station, with 1/8" TRS audio in and out, sound card is the onboard IDT High Definition Audio).
Everything seems grounded properly. (Perhaps that the problem?)
I've heard that computers and audio don't really get along all that well.
Is there a set of steps I can follow to make this go away?