The Song Fight Bulletin Board

So I'm re-recording all my old SF songs (well, some of them), and I was working on one that has like 12-18 a cappella vocal tracks in it. And now in redoing it there's a ton more noise in the audio tracks.

Exactly the same equipment, from mic to PC and everything in between
Upgrade from sonar 4 to 7, but all settings the same

I'm using the same project file, even, so the effects settings are the same. I muted the original vocal tracks and copied them to make the new tracks. When I go back and forth between the old and new, the difference is unmistakable.

Despite this, I've tried changing levels, plugging and unplugging shit, moving the mic into a different room, all that regular stuff. Earlier today I bid on a power conditioner on eBay. Maybe that will help.

I'm getting two different hums and some rich and complex hiss as well. Both are rich enough waveforms that using software to remove them isn't proving satisfactory.

So..... ideas?

ground lift might help (some direct boxes have this)
the power conditioner is a good idea regardless
noise gate would help (but you'll still get the hiss and hum while instrument/vocals are playing)
If there is a compression unit, change the ratio.

If you've recently added your computer to your stereo system you will definitely get a hum. Thats usually on the stereo receiver end though. There is a device for that called a <a href="http://www.radioshack.com/search/index. ... or%20&sr=1" target="resource window">ground loop isolator</a> That would go on the computer output to wherever. (In my case a splitter to my speakers and a headphone amp)