I have the same problem as described here and have tried almost every suggestion I could find on this subject. Nothing really helps. Until I ran into a problem of low speaker volume. One suggested that maybe the phonejack is dirty and there is a shortcircuit in there.
I thought, let me try if I hear the buzz also on earphones. It wasn't in the earphones. When I removed the jack, it wasn't on the earspeaker anymore also.
Can it be some dirt in the earphone jack? Worth to try.