Good theory, but I have recorded many many things before (as I said, this software is REPLACEING an older hardware recorder i used) and never has this occuered in the past. If there were a built in mic, I'd have experienced something like this long before now, so that can't be it.

This is why we try to use dedicated sound cardfs for things like this :)
Anyway. be sure everything is off in whatever app controls your sound card. Then record, then normalize. Hopefully you dont see anything but line noise. Now go back and turn on the input that comes from your kb out. if it works, great, just means there was a mic level in that was activated in your sound card's controller.

As an aside, you certainly dont need a microphone to capture accoustic sounds. Given enough amplification, a regular guitar cable can mic a snare drum, no joke.
Not that youd want this, but Ive seen it happen.
Transconductance happens anytime something affects the difference between the + and - termina;ls of an input stage.

You don't happen to have a Logitecg camera or such plugged in do you? And my monitor has a mic too .... I often forget to turn either of these off....

David

Try this as a test, unplug your headphones
GW

Sounds like you haven't fully setup sound forge if you didn't have this problem previously. Go under the "preferences" menu item and see what you are using as your "prefered recording device" and "prefered playback device". Sound Forge usually defaults to "microsoft sound mapper". If this is checked. 1 you are not using the best driver for your sound card and 2 it is possible since sound mapper is a mixer that you are recording more than 1 device, and if your computer has an internal microphone this would be enabled in your sound mapper mixer. Set the prefered recording device to your sound cards line in input in this field. Also, if you know how to bring up the microsoft sound mapper mixer and go to "preferred recording devices" you can "mute" the microphone input and also raise the volume of your line in input if it's too low. There is a detailed description in the "Quick start" of sound forge called "Setting up Recording devices", that tells in more detail how to do all these things I mentioned. Probably would have taken you the same amount of time to read that section as it did to write this post. Sorry I'm just assuming that you didn't read that section.

Good luck,
Brian Franz