I am re wiring the boat and was wondering if the unit should be grounded from the back of the head unit . There is a small screw there that is for earthing wire to be attached but never used it before . part of the reason for a rewire is due to the 587 getting a lot of noise on the screen when running on low frequency 50k . Not a problem on high 200k. I know there is a fuse in both the + and - wires in the wiring loom but not sure if the additional earth connection at the back of the unit is required as well . Would it cut out any additional noise on the screen .
I have tried all sorts of settings suggested by members but don't seem to get as clear a picture as those posted by others .

Thanks for any help
Paul