[TowerTalk] RCS4 Antenna Switch - Noise

[K0YR]

TT,
I inherited a RCS4 Antenna Switch from an estate.
When first installed it generated noise when using the 1,2 or 3 switch 
positions. The default is #4.
Did some Google'ing and found discussion about corrosion on the SO239's 
mounted to the base plate.
Ran a ground wire across the SO239's to the circuit board. Cleaned up 
some of the other connections.
All seemed well and much improved. This past weekend the noise returned 
and was sometimes intermittent.
Switch is located about 450 feet out at the towers. Fed with 7/8 hardline.
This unit was manufactured in 1992, so could be anything.
Any thoughts on what I may be missing or failing in the switch to 
eliminate the noise.
Tom, K0YR