The new gas valve did the trick. I had replaced the ignitor which had been not always working, but this blowtorch sound became even more common. Then I realized the sound was from flame in the air adjustment area of the burner. Also a small flame persisted there long after the oven was off. Clearly the valve was not shutting off, so I shelled out the big bucks for a new valve. Easy fix because the gas lines screw in and seal without putty and I appreciated reading that you need to crank down the nozzle a couple turns if you have lp. Literally a 10 minute fix and the problem is solved.