I was on a drive today on a small twisty forest road (about 10-25mph), no radio on, window open - and I could easily hear the engine pinging in low rpm going up hills. The pinging stops when the revs would go up and it didn't appear to ping when under load or heavy acceleration.
I only put 91 Premium fuel and the vehicle has about 2300 miles on it (P400). Is this normal for this engine? This is my 14th vehicle and never heard a new engine pinging before. Any insights appreciated!

 

Not normal, at least in my experience w/ the P400 motor.
I would get another tank of fuel from a different location though, before trying to diagnose further... as perhaps you got a bad batch / poor quality tank of fuel.