Erik ,
thank you for your help

here is what i have done

1)i connected ground of inverter to earth
there was no help

2)then i connected ground of my encoder card to earth - this reduced the noise a little

3)i put a line filter in front of my controller card - this reduces a little more

4)then i connected motor chassis to earth
this removes noise problem

note : although i m electronics engineer since 14 years - the most difficult issue to me is electrical noise to understand

if you have more suggestions - please write to me

Mehmet