In the English version? I never noticed.
Yes, English version. It first happens in Skellige, like somewhere in the middle of doing that area if I recall right.
Maybe it's easier to notice if you use relatively expensive headphones and have a lot of experience with stuff like classical music and listening to things carefully, but it was very noticeable to me. The main voice actor for Geralt has a very characterful voice and is superb for the role in general. The replacement sounds flat and lame in comparison.
I've read they forgot to record some dialogs with the original voice actor so they had to use a replacement for parts of the game. I don't have a good source for this claim, but unless I was hallucinating - and other people seem to have commented on it too - then it's a real issue that they didn't fix for some reason, and I'll hate them forever for it.