Lienly,
Also be aware of the possibilty of resonances from the piano, either from the strings or woodwork. If you notice some odd ringing or other coloration, try placing towels over the strings in the piano (temporarily) to deaden them. I had to do this with our upright piano since I could hear a strange ringing after loud passages in movies and music. Drove me nuts until I figured out that it was the piano, and the towels did the trick.
