We visited the Sistene Chapel and the tour stops right outside the room and the guide is very clear "Be quiet and absolutely no flash photography" and then you walk in and its absolutely packed with people being loud and taking flash pictures.
My experiences differ from yours. I've been to the Sistene Chapel twice in the last five years and did not see any flash photography. The guards were very active in making sure people weren't taking pictures and even checking on people with cameras out to remind them not to take pictures.
It did get fairly loud in there because of the sheer number of people in the room. The guards would try to "shush" people now and then to lower the volume, which did help, but not for very long. Individual people weren't loud but it was so crowded that the overall volume was loud.