This sound problem just started for me about a week ago while watching Youtube videos. Xcode is not running. Catalina 10.15.7, iMac (27-inch, Late 2012), 3.4 GHz Quad-Core Intel Core i7, 32 GB 1600 MHz DDR3 Restarting coreaudiod fixes it temporarily for me. My MBP13 with Big Sur 11.2.3 works just fine.