I am also having the same exact issue. Audio sounds extremely distorted after starting SteamVR and sometimes my mic is either much higher or lower pitch than normal until restart.
-I am on a desktop.
motherboard is an ASUS z-170
processor is an Intel 6700K
GPU is an MSI GamingX 1080ti
32GB of GSkill Ripjaws DDR4 RAM
OS is Windows 10 Home
-I was on Beta branch when this first started, but it happens on the main branch too. All firmware is up to date.
-"Speakers (2- VIVE Pro Mutimedia Audio)" is the distorted device ["Multimedia" is mispelt as "Mutimedia"]. The Nvidia audio sounds normal when it works, however sometimes is it completely silent when enabled or it is not detected at all (in both Windows and Steam).
-All link box cables came with the HMD, my linkbox-to-vive cable broke and HTC support sent me a new one, so it is still official.