Electronic humming from alternator

[twack]

I did the saturn alternator swap and have been driving on it for a few days now. Last night i was doing some things and i heard this really faint humming/whine from the alt when the car is OFF. it is always there and is definatly coming from the alt. What is going on? This is with the car off. No codes thrown.

[HiImBrian]

I swapped a motor on a beetle a while back and after everything was done and set there was a humming I thought was from the alternator. Turns out it was just the water pump. If it's not that, I'd double check your wires.

[twack]

This is with the engine OFF not on. Also if i unplug the alt plug it stops

[Febo]

bad altenator?

[HiImBrian]

This is with the engine OFF not on. Also if i unplug the alt plug it stops

ok, if you unplug the alt and it stops that's what it has to be. But, my issue was the same as far as the car being completely off.

[twack]

It does charge

[Kracka]

Sounds very odd. Might be worth getting that alternator tested (or just replace it).

[twack]

Ok well i just talked to the guy who made the original write up on this swap and he wrote me:
"The power wire needs to be changed to a switched 12V source."

[4g63tcrazy]

So it's gotta turn on with the key?

[Febo]

easy, just put a relay on the 12v line. Done and done.