Call them out on it when it happens.
"We just hit the gong and you guys are back at 50 sound, whatever you were doing was wrong. Figure out what it was and fix it."
I'm just flabbergasted at how many people refuse to take personal responsibility for dying. Every single pull that I die on I'm looking to find out why I died and if there was anything that could be done to prevent it. I'm not the raid leader, I just do that because I don't like dying. I don't like being the person that makes the raid fail. Do people like failing?
I mean after a couple pulls of dying to 100 sound you would think that they would have at least some thought to the effect of, I just got insta-killed maybe I should figure out how to make that not happen.
There was a 10 man group in my guild that wiped on Purtricide normal mode 43 times before the OT finally owned up to the fact that his UI was hosing him on using the Abom. I wasn't in the group at the time, but when I asked the members of the group why they didn't change sooner it was because the OT wasn't taking responsibility for the problem. All it would have taken was, "I think my UI is messed up or something" and someone else would have tried and it would have been done. Are people really that afraid of admitting that they failed?
Failing isn't inherently bad, even on fights you've killed a thousand times. Things happen, but you only make it worse when you don't own up to it and fix the problem.