I think what others like Carolina and TennisCJC have said is the general wisdom of using polys... drop the tension. In my case, I dropped it drastically from 50-53lbs to 30+. I'm a former 6.0 collegiate now 5.5 player who hits about 10hrs a week with 4-6 sets of singles and the rest doubles. I hit with moderate spin pre-poly and now hit more with polys. It's part of why polys are used. Polys allow players to hit the ball harder and keep the ball in, so logic dictates that there is more effort in hitting because there is more access to spin.
When people say nothing has changed, then they're just not as conscious about it. The physics needed to hit the ball to a certain depth at a certain speed doesn't change, how it is hit does with various variables like string, racquets etc.
Muscle memory remembers how a certain stroke is swung to get a certain result, and if the result isn't there, we adjust. So there can't be the "same swing."
Perfect technique obviously does not give one immunity from injury. ANY repetitive hard impact motion can possibly cause injury. And being a pro doesn't mean the technique is sound or they are immune to injuries. In fact they are more prone to injury because of the continuous rigorous play. The more advanced the player, the more likely it is there is injury or aches and pains. Par for course and all that.
Funny you should mention sound. A few tennis players have commented that my setup of RPM/Gut @ 30+ lbs is actually more muted than other strings, so much so they have difficulty picking up what serve I hit by sound alone. The brushing noise of a heavy slice serve is muted. I never really noticed it but hey I'm never going to return my own serve. I personally think they just go to one too many loud bars/clubs and have hearing acumen.