A Charleston pronunciation

[Alan Baragona]

A good friend of mine from Charleston, SC, has a pronunciation that even he recognizes as unusual.  He inserts a y-glide between a velar, voiced or unvoiced, and [ar], so he pronounces <car> [kiar] and <garden> [giarden].   He says his mother pronounced them this way, and she was born and brought up in Charleston, too, but nobody he knows outside his family, even in Charleston, seems to have this pronunciation.  Is anybody familiar with this phenomenon and know where it comes from?

Thanks.
Alan Baragona