06 Noisy Cluster?

So I thought I had some engine noise, at idle speed... kind of sounded like a developing knock. Odd enough though I couldn't hear it under the hood at all, just when in the cab/interior. Since I have the 100k powertrain (GM Certified Used) warranty, I took it into the dealership this morning. The tech said it's not an engine noise, and these cars are "notorious for having a noisy motor in the cluster", which would explain why I cant hear it under the hood.

I found it odd that they said there was nothing they could do (even at a charge), so I was on my way.
I guess I just wanted to make sure I didnt have a developing engine problem that was going to cost me money down the road.

Does this sound legit, or was this guy just BS'ing me?