Sherlock Holmes needs clues

I have determined by listening to many different solo piano CDs that something unpleasant is happening consistently across all CDs whenever the piano plays in the octave between about 500-1000Hz. The beautiful warm, natural piano sound becomes somewhat thin and tinny, as though the piano needs to be voiced. Both above and below this octave, the piano sounds warm and natural. I would like to isolate the component (or resonance, or room interaction) at fault.

I plan to play Sherlock Holmes a bit - but would appreciate any thoughts people might have to assist with my learning curve.