Ok Bill, I think that solution may be temporary but it does not end with the problem.
I have to continue investigating where the microfonics arises and how to solve it, because this effect is a failure of something that I have not yet located.
No circuit / componet must modulate the original signal by mechanical vibrations as it is in the case of the microfonismo that drives me crazy.
I also have to try to replace the electrolytic coupling ceramic capacitors to avoid the piezoelectric effect.
I will continue in the matter.
Thanks for your observations.