km,
The 80 knot blast came straight into the cockpit and was amplified by my mouthpiece
This may not be the case for your flight, but I had a similar problem in a Stearman earlier this year, where the noise was coming from the instructor's mike. He had a "hot mike" but mine was a "push-to-talk intercom". Of course, when I pushed the button, the noise was even louder!