Actually the pronunciation is Mur-vul with the Mur being very long an drawn out.
There are subtle differences in regional dialect. I believe I have heard it both ways.
I have a cousin raised in North Carolina doing a year of Christian mission work in Portland, Ore. She has found that some folks will engage with her just to hear how she talks.
“Actually the pronunciation is Mur-vul with the Mur being very long an drawn out.”
Correct, Lady Heron: Murr-vul.