Dis-connecting headphone jacks have a switch contact inside that cuts out the sound to the speaker and routes it to the headphones.
Plug some headphones in and see if it is doing the same thing.
A.If yes then it is probably a circuit board level problem and needs to go for repair.
B. If no, try plugging in and un-plugging the headphones a few times to see if some dirt or corrosion has gotten on the switch contacts inside the headphone jack. I would face the headphone jack down while doing that to see if any debris falls out of the jack.
If the above is not the case then send it in for repair.
Now a wild outside chance is that you are not GB'd correctly & if you have the sensitivity cranked up high, you may see a momentary negative number(very fleeting)and, not hear that response if using the speaker with a lowered volume level. This would be caused by a very weak ground falsing. So only applicable if you are seeing negative numbers.
HH
BarnacleBill
