I have a 2003 Acura TL with ~200k miles and an automatic transmission. Recently, I noticed a whirring noise at low speeds <20mph, but only while coasting. The noise goes away if I hit the brakes or if I hit the gas, even if I manage to maintain the speed below 20mph. Any thoughts on what this could be?
It’s probably the over-riding sprags on the one-way clutches Honda uses in their automatics. To avoid patent fees to Borg-Warner when Honda was entering the car business, they developed an entirely different transmission that does not use planetary gears as all other automatics do. Superficially it looks like a manual, but it does not operate like one. Honda Automatic Transmissions
For the story of Honda’s development of its Hondamatic transmission, in Honda’s own words, see Honda: The Hondamatic Transmission