About a week ago, I noticed a high pitched tone from my ecodiesel when I was accelerating or going up hills at highway speeds. It came in around 2000 rpm. I did some searches on this. Lots of people are hearing a sound like a gas engine pinging. My sound is nothing like this. It's a constant high pitched tone that goes up in frequency as the engine speed increases. I took it to the dealer. They heard the tone, but couldn't find the problem. I was told to keep driving it until I get a fault code. Has anybody else had a similar problem? To me, it seems like it could be the turbo. It spins fast enough to generate this tone, and it works harder when you accelerate. Should I suspect anything else?