Unfortunately I'm experiencing the same issue as Mullet. When Volume is low or no music is playing
I sometimes hear a pulsing noise lasting one or two seonds.
There also is a frequent crackling sound. Those sounds aren't very loud but quite anoying. Only the left channel is affected.
I double checked every chip for bridges though my magnification isn't sufficient. I held the PCB against a bright LED lamp.
There was nothing suspicious.
I used 99.5% isopropyl alcohol for cleaning. As Mullet indicated his problem was solved after he had replaced U9 with LMH6643
and swapped U5 plus U7.
Could this help in my case too? It's hard for me to get replacement parts. A Mouser shipment to Germany costs me 30$.
Somehow I managed to measure DC offset. It reads -1.5 mV on the left and 1.2 mV on the right channel.
This is really frustrating since I put so much effort in it but I got excited to early.
I have no experience with desoldering so I fear I end up with a bricked pup in the end.
Edited by Blanko - 5/15/13 at 2:39pm