I think you're right with it coming from cunnilingus, but I think with having "metal" at the beginning changes it from stimulating the clitoris or vulva to "Stimulating Metal" or something pertaining to that. Something having to do with the sound is so amazing, like feel of cunnilingus.
It's something I thought of a ways back, possibly before the album came out, but never thought of posting it.
H-D