I am working with my teacher on recognizing notes played harmonically. She plays two notes together and I need to sing them back to her. The problem is I sometimes hear notes she is not playing, and they sound louder than the notes she is playing. 

For example - she will play F4 and C5 and I will hear a very loud A4 and my mind will get stuck on it and make it impossible to hear the other notes.

Does anyone else have this problem? What are some effective exercises to get over it?