Engine issue?

Im on my 3rd week with the new 2011 Regal T01. Anyone experiencing with the turbo engine whether stopping at a stop sign or red light, or even the car idling on the drive way where the engine creates a rumbling-like noise that can be felt in the car? However, when driving there has been no issues of this sort. This is something I would have noticed at the time I was test driving the car... so, I reasoned if the car was using premium gas by the dealer, and if that is what they call "knocking" or "pinging" when using a lower grade gas?? I did fill the tank with 87 octane on the first week, then changed to Premium by that weekend. On the 2nd week of a another fill-up of premium and would think the gas tank is now 100% premium, but there still is that issue? I don't know what an engine knock sounds/feels like or if that is what I am experiencing? I'm thinking of taking it to the dealer, but would have like some feedback first.