I had a Soundcraftsman 15 band per channel EQ that added noise to my system.
I now have a Harman Kardon EQ8 that is dead quiet when in use, but....
I had a guy who's a professional musician, piano tuner etc. play with it for over an hour. I tested it on and off with his eyes closed. My system sounds best with the EQ8 off and the tone controls in the neutral position.
The EQ8 is put in line to redo bootleg cassettes and such to record them to CD's.
This has been my experience, yours may vary.
Like most things, EQ's have plusses and minuses.