Motor noise would make communication even harder. ...............Bill says; "Don, change frequency to 123.5", then shortly after that, Bill detects thermal activity and says " You got it", meaning he wants Don to fly the ship as he shuts down the engine. Don replies, "yep", meaning he has changed the frequency. Who's flying the ship? NOBODY! Don was an experienced fighter pilot and he would have said, "I have the aircraft "and shook the stick, if he was assuming control, but he wasn't. When Bill didn't get the proper response, he should have re-stated his request.
JJ