Battery Isolator noise

Open the housing slowly as there should be a spring that actually closes the contacts

Thanks for the info. I will let you know if I have any success with your info. I cleaned all the battery connections today and made sure there were no other simple problems that I could have missed. Again thank you so much.

I have the standard Intellitec latching relays.
I have had to clean the inside.
The relay should not hum.
Power should be applied to latch the relay. Then power is removed.
I am guessing the contatcs are corroded or pitted.
You can disassemble the relay and clean them.
I would also check to insure the power is disconnected from the relay coils. If it does not disconnect the switch could be bad. You can test by latching relay, then disconnect one of the wires from the small post. If the hum goes away your switch maybe bad.