I believe the Bafang bbs## mid drives are the quietest of DIY motors, and the only ones I’d personally consider. The tsdz is probably in the middle of the pack for noise. I couldn’t handle that, but you suggested a friction drive, which would be equally irritating to me.The TSDZ2B sounds much louder than the Bafang. Is that because of bicycle + camera positioning, or is it a noisier system?
I like trail riding with a silent ebike, since I get right up close to the animals near the trails. I’ve ridden within a couple feet of deers lying around by the trail, and have had to push cattle to the side when riding on trails through pasture areas.