So, just to close the loop, I think I know what was causing the whistling. I'm not quite sure why it started when I changed the wipers, but whatever.
It was not the wipers. In fact as part of my investigation, I removed both wipers(after trying both the Tesla and Bosch(I know they are identical to Tesla!) and even Trico brands). Notably I didn't put a spacer to hold the arms up an appropriate distance in when I removed the wipers, which might have been a good idea to precisely match the arm position. The noise persisted, so I put the wipers back on.
I then tried some gorilla tape(this was not intended to be a solution, just an investigation!), splitting it down the middle or thereabouts to make narrow strips and covered the rearmost lip of the cowl where it met the windshield. Additionally, by some stroke of luck I happened to touch a black piece of plastic that seemed to be loose. shown with some all-weather tape(
https://smile.amazon.com/Gorilla-Weather-Waterproof-Temperature-Resistant/dp/B07GRJ8L55/) on it now. Initially I just used the same 'standard' gorilla tape.
Went for a drive, and for the first time in seven months, my whistle was gone!
I removed the cowling tape and drove again, and the noise remained gone!
Today as I was driving around I noticed every now and again a little chirp out of the same area as before. I assumed the original duct tape was starting to loosen up, and when I got a chance I took a better look at it. It appears there are at least three barbed spots on the plastic that were supposed to be grabbing the hinge, and one of them wasn't attached, it didn't seem to want to stay clipped in, so I added the all-weather tape as shown in the picture. The lowest clip(hiding inside the tape now) was the one that wasn't gripping.
I haven't taken another drive yet, but if I hear the whistling again I'll probably remove this plastic piece completely, as yet another experiment. It appears to be purely decorative, to hide that 'unsightly' hinge