Low volume on Macbook Pro 2011 (Early) after upgrading from El-Capitan to High Sierra

I have recently upgraded the O/S for my macbook from El-Capitan to High Sierra. The volume is now soft like how some people actually complained/reported about.

I found that the softness is due to the sound now coming out from the MIC instead of the speaker.

I have tried all the recommended fixes like PRAM/NVRAM reset and the problem persist.

Wondering why this is so with the audio and mic now sharing the same I/O device ID/Channel perhaps?

Hopefully the Apple support can advice. If there is actually hardware incompatibility, then it should be noted and I might just revert back to the older version.

Thank you.