So this happened a few weeks ago, I was doing a Zoom meeting with family and the microphone would not work, no one could hear me and I was unable to get it to work. Later, I checked system preferences however the input level is unresponsive, unless I tap on the case, you can see the bars move. Siri hears me ..very faintly, and what I ask isn't answered. I have tried FaceTime however the mic on FaceTime is muted however the person can only hear me very faintly.
PRAM and SMC was done, no change. I then called Apple... however couldn't help me, so the iMac went away to an Apple repair shop where the logic board was replaced. It came back today and after a fresh reinstall ... its doing the same thing, am just completely lost for words ...

HELP! What is going on??