I pronounce it with a "-line" ending rather than a "-lyn" ending. It's my mother's name and she's constantly called
Carolyn too (which she hates). We're from the
UK so I don't think it's anything to do with not wanting to sound like hicks (here anyway). I agree with mirfak that it's often likely to just be a careless error in pronunciation.
I love the name by the way, I hope to use it as a middle name someday. :)