Most unusual as these are only wav files! sh3.sdl file is sh3's mixer, & if only some of the sounds are stuffed you would think that it would be this file or the wav files themselves!
Just a thought but does your "sound card/onboard sound" have settings in control panel? maybe a mixer setting here such as echo! or you could check the file type associations to the wav file,
if I think of anything else will let you know!
Reece.