Possibly nothing. Some scallops are sold "wet" -- coated in a chemical solution. That might have been what you tasted. (Yeah, yeah, they'll tell you that it's tasteless, but almost NOTHING is totally tasteless. :rolleyes: )
Try rinsing the scallops in salt water next time and pattingthem dry on paper towels before cooking them.
Then again -- how dark did you cook the garlic? If you let it get really dark, it might have burned, and that gives the whole dish a bitterness.
"Notorious stickler" -- The New York Times, January 4, 2004