I purchased a small USB audio adapter so I could use a stereo microphone with my iMac without needing phantom power. Plus I would get higher quality recording. It worked brilliantly the first time. Clear sound, no background noise or interference. I unplugged the audio adapter for a bit and then later I went back to record. Now when I record there is this buzz-like high-pitched whine that comes through all the time (you can hear it after recording and if you turn on the audio monitor)... it can still pick up other noises but the entire thing is permeated by the whine. As soon as you either switch off the microphone or unplug it the whine disappears. This occurs on both my stereo headset and an XLR microphone I've tried with an adapter. Both can record fine, but there is the high pitched whine over top of it. What's interesting is there is no whine when recording with the little microphone in the iPod earbuds or my Sony earbuds. If I unplug the microphones, and press my finger to the audio in port on the adapter or hold my hand anywhere near the adapter, the whine returns. I take my finger off or pull my hand away, and it fades away. The whine only comes out of the left speaker (or headphones if I plug in headphones)... in fact, for some reason, it won't record through two channels, or my iMac isn't playing out of one channel. It worked perfectly the first time. What the hell is causing the whine and how can I get rid of it?? I need to record! [Edit]: here's a recording of the whine.