The tribe of Ephraim had a pronunciation peculiarity that distinguished them from other tribes - words, pronounced by others with an "sh" sound, were pronounced by Ephraimites with a simple "s" sound. This peculiarity became a deadly marker after the inhabitants of Gilead defeated the army of the Ephraimites and proceeded to slaughter the survivors. Those attempting to cross the Jordan river to safety were forced by the guards to pronounce the word "shibboleth". Those who could only stammer "sibboleth" were immediately killed.
Thus we see that at one time, people took pronunciation seriously.
As long ago as the 1990's, when rap music spread across the musical horizon, I noticed a peculiarity of pronunciation in many recordings. Words beginning with "str" were clearly being pronounced as though they were spelled "shtr".
Thus, you might hear what sounds like "I shtrap on my rod, I shtrut on the shtreet, I look for the shtrays, Aim shtraight for their feet."
I suppose almost any minor language variation, given the right prominence, can be picked up unconsciously and repeated by others - after all, that's more or less how we learn to speak in the beginning, and it's how people renew and refresh their language, how Northerners who move south gradually pick up a partial Southern accent that seems to amuse both their old and new friends.
As some evidence for this not quite imperceptible language change, I mention a few occurrences:
"He's very good at dishtracting people. He can't run on hope and change anymore, so he's running on division, dishtraction and dishtortion to try to win an election by default."
"The space shuttle will go on dishplay at the Los Angeles Science Museum."
"A boy in Athens killed himself after shtruggling with depression for five years."
"[If] Tony tried to shtrike at them again, we should take him out."