Cat,
is the shs sound hear from 1 speaker or both speaker?
check your soider point (connection point) of the component u had chnage. Sometimes if not soldering good (dry solder) when temperature increase then the bad solder point may have bad contact (expansion of metal) n can cause the noise too....
But i will check the grounding point, for screw type sometimes they may oxidize...
or the old solder is internally crack but outside can't see....
too many possibility....
sorry my knowledge in this is too little can't really helps : (
