audio echo problem

Hi all, I am running Windows XP SP2, with both an on-board soundcard (Asus
p5nsli board) as well as also owning a Soundblaster 24-bit PCI soundcard. My
problem is that about 3 days ago I ran Company of Heroes off my old hard
drive without reinstalling it first (I recently reformatted/reinstalled XP),
and it did start up fine so I thought everything would work ok. BUT, it
appears something got stuck in the wrong setting or whatever, and now in
every program I have a weird background echo. It's a delay of about 3/4
second, and if I stop a sound quickly I can hear it echo twice, so it seems
to be a reverb setting. However, I can't get rid of it. I restored to a week
ago, hoping that would fix the problem, and it didn't. Then I took out the
soundcard, reinstalled the onboard card, and the problem is still there even
though the sound drivers are different. Which makes me think it is something
that's been changed in the Windows files. Anyone know how to remove a pesky
echo like this? Perhaps a file to re-copy? Or a setting somewhere I can find?
I've gone through all the standard menus for audio, and haven't found
anything.