Read this if you are using Samsung phones with Bluetooth (2006 models)
 

My Samsung x820 ("Ultra 6.9") went into some sort of a feedback loop with itself when I answered a call using hands-free. Stock hands-free on 2006 S4.

That's an experience not too dissimilar to getting an air horn blown directly into one's ear without any warning, all while driving in a dense traffic.

Just FYI. Otherwise - it's a great phone.<ul><li><a href="https://forums.audiworld.com/canada/msgs/133169.phtml">(my other post in Canadian forum)</a></li></ul>

A follow-up
 

Updated both the RNS-E and the phone to the latest available firmware. No go, the phone still resets itself when trying to accept incoming call.