Had a similar experience the other day on the highway. Traffic was doing ~85mph so I was too and got passed on both sides within inches of my side mirrors by a group of 8 or so people on racing bikes with loud exhausts doing at least 100mph. I didn't hear them/notice them until they were basically in my blind spots, it was very unsettling.

I also suspect that the bulk of exhaust noise is projected to the rear of the vehicle anyway, which makes it not especially useful as a "safety" feature if you are unsafely driving considerably faster than and weaving through traffic.