AND WE HAVE A WINNER?

xr4racer was correct - the washers (Mazda calls them isolators) I got from the place that cleaned the injectors were too big - they literally would slide off the injector. I got some genuine Mazda ones and it purrs like a kitten. They did not leak gas because there is a vacuum there - the sound was the air being sucked in and the washers acting like reeds.