08 CX-9 and engine knock

So I have been hearing a low grating sound from my engine at certain RPMs. I thought it was in the transmission. It's been doing this for about 2 or 3 weeks now. I finally got a chance to bring the car in to the dealer. The dealer is now saying that it's engine knock (or pre-ignition). I can't believe this! The car only has 8K miles on it. The dealer also asked whether I've been using premium?! It takes 87, I told them. That's one of the reasons I bought this car.

So my concern, even if the dealer can fix the problem, is whether this would have damaged the engine. From what I've read on the internet it can cause premature wear on the engine, especially since it's been doing it continuously for weeks.

Any inputs??

This won't be the first time that dealer was wrong.
Try a tank of 91 octane just to see if it makes any difference.

I appreciate the input, but I shouldn't have to use premium in this car...if i have to resort to that, I will demand that Mazda take it back.

Agree. You shouldn't have to. Use one tank to see if that indeed makes a difference.

Dealer called and said it's the vacuum hose booster bracket..was loose. We'll see...

08 CX 9 and engine knock

Use real oil. That actevo crap is crap...

And yes there is a knock in these motors...