Totally understand the point.
To be fair, we have the technology to allow a combustion engine to run at it's most efficient point at almost 100% of the time - that's what a CVT gearbox is for. When Williams tested that it was rumoured that even during the first on-track tests, it was several seconds a lap faster. Some electric motor advantages are genuine, whilst some are because the equivalent technology for an ICE has been banned. We'd get improved fuel and performance from ICE if we opened up the regulations in that regard.
I totally accept the point that the noise is a by-product, but I do think these things are important. Visuals are also a by-product, but that doesn't stop regulations outlawing stupid nub noises, stepped noises and similar odd appendages on F1 cars. There's no reason for dealing with that other than aesthetics, and noise is a type of aesthetic. I honestly don't have a problem with some sort of regulations which help improve the aesthetics. But even ignoring that, the current regulations aren't great for diversity. The GT regulations heavily favour smaller engines with turbos - so losing the sound is a by-product of decreased diversity allowed by the regulations, which is a shame.
My problem with the lack of sound isn't that we'll lose it from one car. It's that we'll lose it from all cars. Less atmosphere, less diversity and less personality.
In regards to Audi, the fuel cell stuff is interesting because they aren't pushing that in road cars as far as I'm aware. So unless there are projects in Audi they aren't talking publically about (although they do tend to talk about these publically, to show positive steps post dieselgate), then I'm surprised Audi would look at that for racing.