Batterys Dead / Alternator buzzing noise

[sktruiybm]

Truck is a 2000 excursion 7.3.

If left for a day or two the batteries will be dead and my truck will not start.

I noticed that when the truck is completely turned off the alternator still makes a buzzing / humming noise. if i disconnect the connection with the two smaller wires the buzzing stops but the battery still drains but it seems to take longer.

I'm thinking it could be a stuck relay or something?

The alternator is fairly new (less then a year old) and the batteries are also fairly new - red tops maybe a little over a year.

Sorry if this has been covered - I tried searching and couldn't find anything...

Anyone have any idea what may be causing this?

Any ideas would be greatly appreciated.

Thank You

Sam