At what point in the process are you detecting these flavors? Are you noticing them while sampling in the fermenter, or in the bottle under 3 weeks...or longer than that?
It is really difficult to figure out whether you truly have an off flavor, UNTIL it's been over 3 to 6 weeks in the bottle (or kegged) there is too many processes that that beer still have to go through, which will change the flavor (mostly cleaning up stuff like that) which won't be complete till the beer is carbed and conditioned...otherwise the beer could just be green and young...
Most of my AG beers taste grainy and somewhat nasty until the condition.
As to d-rests, this is a good thread...I even posted some stuff at the end on D-rests for ALES as well as lagers. http://www.homebrewtalk.com/f13/prev...-please-70438/
But if your beer is 8 weeks in the bottle and taste that way, then you could concerned, anytime before that, for me, I would just feel that the issue was greeness and give it more time.