Permanent 50hz


I have 50hz noise from the speakers.
its not the hiss from the tweeter. It’s from the mid. (Rrrrrrr)
the noise is exists even when only the power is connected to the speaker with no source and preamp.
the problem could be from the electricity in my home or it’s the amp

musicland1
If you want to test to see if the issue is the amp you could try putting shorting plugs on the amps inputs. Then power the amp on and see if the noise is still present.
If there is nothing connected to the speaker except power cord, and we are assuming it's a powered speaker, (no RCA or XLR signal cables) -- if you are still getting 50hz buzz, then I agree with Eric that the power supply is failing (probably a bad capacitor).  The amp/ps board in the speaker likely needs to be replaced.
actually the noise is quiet..i need to put my ear very close to the mid unit
from 5 cm I can't hear the rrrrrrr
i don't know if it's normal or not

Not normal and Why would a 50 Hz tone be coming from the mid range driver. The cross over should have taken that out. What kind of speakers are they?
If you have to put your ear to the speaker to hear any artifact its quite literally no concern. Almost any amplifier will have some audible artifact in that situation.
Don' worry'bout it.