Way back in first year music theory at university, we were going to spend much of the semester analyzing Mozart's K540. My prof came in day one and "you are going to learn how to describe music in a technical way. If anyone writes 'the piece starts off smooth and flowing', you will fail."

Similarly, the better you can describe problem areas to your Mastering Engineer, the better result you are going to have.

To spark your imagination, I have listed some adjectives below. I think the words are fairly self evident. Each of these words has a resonance that corresponds to a particular frequency range. If you can accurately pin what you're hearing down to a couple of these words, that will give your mastering engineer a place to start looking for what you would like to address.