No, it’s the conversion: normal film speed is 24 fps and PAL is 25. It’s much simpler to just speed everything up by 4%. There is no other “proper” conversion that exists except for digitally altering the pitch of the soundtrack but that’s more the exception and not the rule.
I think you’ve just now noticed it. I’m in PAL land and I have a hard time watching DVDs because of this. Thankfully Blurays don’t have this problem.