Dear Mr. Moreno,

it is difficult to answer.

Did you sent one of these drives to the repair service in order to see what is defective?

Please check the line supply for voltage peaks and the frequency. (200 ... 240V AC, 47 ...63 Hz are allowed).
IT line supply for non filtered device or TN line supply are o.k.
If influences are comming from the line side a line reactor often helps.

At the output side check the equalisation of the potential between the converter and the motor as well between the control and the converter (analogue source).
Carry out a correct shielding.

Please find the EMC rules: http://support.automation.siemens.com/WW/view/en/60612658

Best Regards