Happened to me in a R44 at about 100kts, but in my case it was self inflicted. Student flying, somehow the conversation came up about a door being unlatched in flight....me being the all-knowing instructor, I confidently told the student that nothing would happen due to the airflow pushing against it. I then preceded to unlatch said door followed by a very loud
. Tried unsucessfully to pull it closed for a second or two, then had the bright idea to reach over and push the fresh air vent closed which thankfully worked. Made sure student understood he was to never to speak of said incident and continued rest of flight.
Live and learn.
Mike