I can make a few suggestions to try to isolate the problem.
Either the noise is what is called "conducted" and coming out on the power cables for the washing machine, or it is "radiated" and emanating from the motor.
What is the distance between the Boltek antenna and the washing machine?
Is the washing machine grounded? I see that Greece uses 230V 50Hz power. Are there only two power wires that supply the washing machine? (in the US we have a "neutral" and a "ground" (called Earth in UK). Is the washing machine housing completely surrounding the motor or is it exposed? What is the material of the housing, steel?
Does the motor have "brushes" and can you see small sparks if you can look inside the motor while it is running?
The only things I can think of at this time are:
- Increasing the distance between the washing machine and the Boltek antenna.
- Some kind of filtering added to the washing machine to suppress the noise at the source. If you are not an electrical/electronics expert I would recommend finding someone who is. Maybe you have some local Amateur Radio operators that could help. They help people with interference from the radios, and this problem has some similarities.
- Improving the grounding of the washing machine. Perhaps a ground wire from the washing machine to a good ground like a metal water pipe or ground rod. Also, adding a flexible ground wire to the motor of the machine might help.
Maybe some others have additional or better ideas.
Greg H.