2000 Expedition ABS noise

Hello,
I have a 2000 Expedition 4x4 with a 5.4 litre Triton. My problem is that there is a loud buzzing noise coming from what looks like a proportioning valve located about 6 inches below the master cylinder. This unit has brake lines running into it, as well as electrical connectors. What is critical to note is that this noise does not stop when the key is turned off. In other words, electrical current is going through this unit when the key is turned off. I have to disconnect the battery to keep from draining it when the car is shut off. This does not sound like a warning buzzer. The ABS light is on too. When I put my hand on the unit it's vibrating strongly, but there is no heat. A few days before the noise started, I put a new battery in. The old battery was tested and was bad. The negative terminal was stripped out, so I put a hose clamp around it to tighten it. Any error here? Any help would be greatly apprecited. Thanks friends!

It sounds like the unit for abs that also controls the auto 4x4 engage when it detects slippage. I had brake fluid drip into the electrical connections, cause a short that made the sounds you describe (but not on my expedition, escape). I'd clean it and the sound/short went away. The fluid reservior cap liked to leak a lot. Unfortunately one time it happened the short, after the vehicle was turned off for 15 minutes, and driven by my wife who ignored the buzzing, started a fire. Insurance didn't cover $600 plus my $500 deductible, but did cover the rest. They don't cover what causes the fire. I'd get that unit replaced.