The phone audio output seems to go to saturation at some frequencies, I can feel hear the sound from the speeker and identify, atleast in this unit. I don't have the proper proof, I even went to Nokia care centre. But failed to explain and convince the staff.
Initially, I thought it's a speaker issue. But when I heard it through head phone also, I am very sure that it is something to do with audio processor unit.
If technical team is listening, kindly look into it.