MS Teams microphone does not work on App only - buzzing

Hi

My MS surface, running Windows 10 has a problem when using MS Teams app for meetings.  It will either buzz noisily for the person on the other end or will not deliver any sound at all.  It works fine for Teams on the web, Zoom and any other application working with a microphone.

I have gone through the troubleshooting steps - rebooting, updating, deleting the Teams cache, reinstalling Teams etc.  I've even tried a different windows profile on the same machine but nothing works. 

Has anybody had this issue and managed to solve it?

Cheers