After joining the Slow ring of the Preview program (as well as the Fast ring, briefly) in a vain attempt to update to 10586.29 my call quality has universally been reported by other people as being horrible to the point of being unusable. Callers could barely make out that I wanted to call them back. While I had no system update available to me via the Insider program I was prompted to reboot my phone as "phone settings or your SD card have changed." On my end I've heard a slight crackling or static during the call. I did a hard reset of my phone afterwards and did not re-enroll the phone in the Insider program afterwards but I believe the issue may still be happening. After the hard reset I received the same aforementioned prompt to reboot the phone to apply settings changes. Prior to enrolling in the Insider program I had never seen that prompt before.
I'm running 10586.0 on a 950 XL on AT&T. This issue happened in multiple locations - the middle of downtown Seattle as well as my home in Sammamish, WA. Please let me know what further information I can provide to help with this.
EDIT: I was able to call to my phone using Skype and record the audio using my computer via direct input (i.e. entirely via my computer's audio system, NOT by putting the microphone up to a speaker or the like) as it sounds from a caller's perspective. It does indeed sound like there's a ton of wind coming through although my environment is not windy and is very quiet. My voice is barely audible through all the noise.
EDIT 2: Using the "Voice Recorder" app on the phone I was able to reproduce the horrible static/wind noise. Looks like this isn't so much an issue with making calls as it is with everything the mic records. Again, this just started.
EDIT 3: Again via Voice Recorder I've found that, as confirmed by callers I've tried speaking with, the audio starts out completely silent and clear of interference. However as the call/recording goes the noise steadily increases. It sounds in this second recording like some kind of static. This makes me think the problem is with the noise cancellation software on the phone. If it were some kind of interference or a poor physical connection then I would expect the static sound would be constant from the beginning of the recording.