Echo and Reverb!

Even starting this topic is frustrating! I was trying to do a webinar today but because of the echo and reverberation, had to cancel a presentation minutes in. I have a MacBook and in order to play audio not only from myself but from the Keynote presentation I have used Loopback flawlessly until recently.

Got error code 10004 so I uninstalled and reinstalled Zoom. Still SIGNIFICANT echo and reverberation. I need to be able to use audio from my mic, Keynote and Quicktime player for audio and video - WITHOUT echo and reverberation. 

Can anyone help solve the problem, or does anyone know of a company/person that could troubleshoot these issues for me?

Thanks,