XPS 9380 (2019), running factory-installed Ubuntu: cracking and white noise when recording using mic

Hello,

I have a Dell XPS 9380, purchased in 2019 and came with factory-installed Ubuntu 18.04 LTS. For a long time, I never used the microphone function but recently, I am using a lot of Zoom/Skype. Problem is, whenever I speak in my mic, the folks on the other end complain that there is a lot of crackling/jarring noises. Therefore, I used to sound recorder to test my mic quality. I hear this noise both with my earphone and system built-in mic. 

I already contacted DELL Services (I have Service Warranty active). But they were not really helpful in fixing the issue. The following were the solutions they provided:

- Gave me completely unrelated audio fixes for Windows devices, like using Dell Support Assist (I clearly told them I have a Ubuntu Laptop) 

- Asked me to turn on/turn off the mic

- Requested me to update BIOS (I already have the lastest version 1.12)

- Requested a system diagnostics from the Boot menu (The check passed successfully with no hardware issue detected; validation code 83523)

- Finally asked be to reinstall Ubuntu

I even updated to the latest Ubuntu 20.04 LTS following the Service person's suggestion. Unfortunately, none of this has solved my mic noise issues. Fwiw, the audio quality from the speakers and earphones are good, without any glitch; its just the microphone function.

It would be really helpful if someone here could suggest me some fix for this issue.

Thanks!