Thanks. So anything that impededs the bracket from resonating. Mine is at 1400 rpmA nylon zip tie might work just as well, or a few turns of self-fusing rubber splicing tape around the connector and the bracket. The main thing is to immobilize the connector block so that it can't resonate, and it doesn't much matter what material is used, as long as it inhibits movement.
Looking down from the top this afternoon, I noticed that a nylon clip holds the O2 sensor cable to the firewall, and the run from the clamp to the connector has no slack.
How much slack exists between the clip and the connector is a variable that might explain why some HRVs have the buzz and some don't.
Like everyone else.