John, if it's the flywheel (MT only) that shows by going over about 3500-4000 rpms then keeping in gear when rpms get to about 2500 it feels like mild rumble strips. That's "normal" not right but "normal" I would ignore it. It's up to you about the rattle. I do suggest that before your dealer works on the car tell them about the exhaust and if they are friendly about that. Good luck and welcome there is lots of good info here.
also w/o insulting is it mild knock at low rpms?
That's a pretty accurate description, yeah. I think I'll let it be for the time being. I plan on taking my car by the dealer in the next few months to get it looked over and talk to someone about a few small issues before the warranty expires. And no, it's definitely not an engine knock. To me it sounds like something loose behind the head unit or somewhere around the middle of the firewall. I can live with it; it's done that since day one.
Airaid CAI, Roush axle-backs, Roush high flow upper grill, Raxiom Smoked Projector HIDs