Piano Middle C

In listening to a vinly LP last night of piano music I noticed that the notes aound middle C were slightly distorted.

I haven't come to a conclusion yet but I have heard piano will reveal acoustic and other problems in a system.

I am assuming that it may be caused by one or more of the follwoing:

1) The recording itself
2) The cartridge (Grado Gold)
3) The speakers (ML ESL's)
4) Room acoustics..

Any thing I may have missed and any thoughts on this?

but, vinyl being what it is, the record itself is always suspect.

Speakers capable of good articulate bass is essential to producing realistic piano sound, system synergy is also necassary. Without the above, piano may sound good but never quite right.