You have to do a better job of explaining the off-flavor.
I'd recommend reading the chapter on off flavors in Palmers book, www.howtobrew.com and narrow it down.
Lambic to me would be sour, but caramel, bready would be a certain type of malt, or yes, just extract twang. Let's narrow this down a bit, and we can pinpoint exactly how to fix your problem.
Are you getting vinegar, acidic? That would be an infection. Sanitation is the obvious issue.