Hi there!
hot this problem too..
If you enabled surround (5.1 / 7.1) in your speakers or your headphones settings just revert it to stereo and every thing will be back to normal
Thanks for the reply friend.
I had to remove the SweeFX from TW3 and reinstall the entire game :(
I already did your method before, but I want my 5.1 sound back. After a "fresh" reinstall everything was back to normal... The sad thing is that I forgot to make a BK from TW3, so I had to daownload everything again :(
I'm using 7.1 and don't have this problem.
And for the record I HIGHLY doubt ReShade would ever cause this problem.
Make sure you are using ReShade though and not SweetFX 1.5.1, ReShade is under constant development so problems like this or similar get fixed frequently when discovered.