Have you tried opening alsamixer in terminal.
View "All" channels [F5]. Have a look at your mic, headphone and speaker channels. Unmute everything and have a play around with their levels and see what you get.
It may be a bit pot luck to find the specific combination of your headphone mic (capture) and speaker (output) combination.
So just discovered this is effectively a duplicate post of this one. Earphone mic issue 