Lee, I had the same type of issues with buzzing/crackling after the 2019.11 update. I thought something in my audio system was failing. Thanks for providing info on some of things that you tried. I had to switch from WASAPI Shared to WASAPI Exclusive before I could change the Mixing Latency Buffer Size at all. I also boosted the Buffer Size up (to 2156 samples). I'm at 44100/24 bits while before I was at 44100/16 bits, so moving to 24 bits did not cause an issue. My effective latency at 44 kHz is now 48.9 msec. I'm using an older Digidesign Mbox 2 interface that I found for $14.99 at Goodwill. At least the buzzing/crackling is gone and I don't have to buy any hardware now.