I tried both the headphone and front speaker outputs into known good headphones. No beep.
The manual does not indicate any speaker on the MoBo. The 10 pin front panel audio connector on the MoBo seems to go to the jacks in the top front of the computer.
Will try the “disconnect almost everything” after supper.
The manual does not indicate any speaker on the MoBo.
See page 2-37, System warning speaker: "This 4-pin connector is for the chassis-mounted system warning speaker. The speaker allows you to hear beeps and warnings."
I think that they should go to a small speakerl in front panel.
The 1/4” is usually for onboard audio