Some interesting developments! I actually had 3 props making this noise, with the 4th being silent. Upon inspection, that 4th prop must be one of the new ones that have a small bit of foam in them to plug the gap between the props and the mount. I found a "fix" on youtube that involved placing a small piece of electrical tape on the inside of the props, to help reduce the gap - and it worked! All 4 props are now silent. AND: To my absolute delight, the
I2 now flies straight as an arrow. Before, it would veer off to the right really badly. For instance, I would try to fly it straight and it would veer to the right maybe 40 degrees. Now, it's almost perfect. I was thinking it might be one of the "bad" ones that just had issues, and it was about to become a really expensive paperweight. So now I might order the Xoar carbon fiber props )non-foldable) and see how they perform.