I have a CT2760 hooked up right now and definitely working, so I was going to check how my jumpers are set, but apparently my CT2760 and your CT2760 are different. So much for model numbers. I don't have any jumpers in that area.

The problem you're describing sounds familiar, I think my CT3990 started doing the same thing a few years ago. I don't know the solution, I am only guessing that some component has failed. Maybe somebody with a matching card can at least verify if your jumpers are correct.

Those jumpers route the amplified output to the speaker jack. As long as you're getting left and right output they're in the right place. It sounds like your problem lies before the mixer stage or in the mixer itself.

I was afraid of that, was hoping I could just disable the amplified out like on the CT1740, and the problem would just go away 🤣 .
If i change the gain to x1 the problem disappears, but the card is so quiet at that point its barely audible at normal listening levels.
This card has a real opl-3 chip, and would love to actually be able to use it.

Yes those jumpers control R, L output tried messing with them.
Reinstalled the card today, and the problem seems to be much worse then the last time I tried using the card 🙁
The sound is the dominant thing you hear over EVERYTHING now, and that is via LINE-OUT, not SPEAKER-OUT.
Another Project I guess for Recapping later, if I ever get around to doing it, what else would cause it?
Defective mixer chip?