There are certain circuits that are
always 'hot,' even when the key isn't in the ignition. I would check a repair manual to see if the ABS is one of them, as the poster above me pointed out. Among other explanations I write about below, during the hammering, you may have knocked a wire to a sensor out, causing misreadings and thus the pump to activate, or the pump could be malfunctioning, etc. Technically your vehicle should start and run fine without the ABS, though you will get a warning light and you won't get any ABS. It seems to me that diagnosing the ABS would be the secondary concern if, in fact, the ABS was the culprit of the noise.
If by 'copper connector' you meant the wire that connects to the battery terminal, I would recommend that you strip that and wire in a new connector. That itself can cause a whine if a very small fracture is arcing. If it is corroded and cracked it can cause all kinds of other strange behavior too. You can get generic connectors for less than $10 at any auto parts store and it's a very simple operation to replace it, they may even do it for you. Expose the inner copper wire either by removing the old connector or cutting it off. You may now have to strip the wire some if you had to cut; large gauge wire strippers (<$10 at the auto shop) are good here if you have no experience doing it. This copper wiring should be clean and shiny; if it is corroded then you can try stripping a little bit off (not so much it won't reach the terminal!) and if that part is STILL corroded, you need a new cable, and this can be the cause of all your troubles - the corroded wire may not be able to transmit enough amperage to turn the engine over. To continue replacing the connector , clamp the exposed wire into the new connector by using the two screws (on most cheap generic models - just follow the directions), connect the wire to the battery (I hope you've cleaned the battery terminal with a steel wire brush by this point), and you're done, in 5 minutes or less, and you have one less thing to think about or go wrong in the future when you're trying to diagnose your problems.
Remember that the terminals on the battery should be bright and shiny. They are, after all, lead.
After that is done, I can't see the harm in putting in a different battery that you know to be good; it is an easy and fast operation that could save you a great deal of time. However, bad components such as a bad voltage regulator could have led to the destruction of the first battery; I wouldn't just leave it at that; I'd perform standard alternator diagnostics.
Actually, interestingly enough, the negative terminal on my battery that I had issues with that I describe in my thread (that tested at 100% charge) had been loose and held on basically only by corrosion unbeknownst to me for quite a while. And the dome light wouldn't go out for anything unless I pulled the fuse for it. Sounds a lot like you...
If the battery is old and has been left to sit, you may have to add water to it or you may even have spilled acid. However it's been many, many years since any major auto-maker outside of high-end sports car makers have used this type of old battery; newer ones (meaning in the last 10-20? years) are 'closed' and 'maintenance free.'
I suggested trying to swap the battery because (a) it is easy to switch out and (b) it can cause the strangest sounds as your vehicle gets power, attempts to 'boot up,' the power fails, it gets it and tries to 'boot up' again, etc. This can happen repeatedly very rapidly. I don't know enough about your ABS module to know if it engages the pump to up the pressure when power is applied after a while of inactivity, but I can certainly speculate wildly out of my ignorance that that COULD cause a whirring noise. Again though, testing that the engine can get enough amperage to turn over is more important, and you start to test *THAT* at the battery.
If you don't have a battery to swap around, the first step is to test the voltage on the battery yourself with a cheap voltmeter or digital multimeter, these are $20 or less at Radio Shack or most auto stores. Don't buy or be up-sold on an expensive one unless you want to waste money or become an electrical engineer; as long as it tests up to 16V, even if it's analog, it's all you need. Test the battery directly across the terminals (put the leads between red-black terminals) when it isn't plugged in and and see that the voltage is within the 12-13v range. Repeat when wired in, it should still read around there, and fall slowly for a while as systems 'boot up' and 'go to sleep' (in modern vehicles there's lots of components that draw load while your car is 'off'). It should not have dropped by more than .5V or so immediately after being plugged in. Then test it after turning the headlights on. If the voltage is below 12V in either situation, your battery is drained (because of a bad alternator, or wiring to the alternator, or various other reasons), you have a leech (short circuit somewhere), or your battery is broken. I would not suspect the whirring sound would be the leech since that is new since you hammer on it. If your car ran fine but has been sitting for a while (esp. if it's more than a month), and especially since the battery seems to test at 83% just by reading the voltage (see way below), I'd think it's a bad (not just drained) battery.
Here is the thread where I describe the weird phenomenon with batteries damaged in a certain way in detail:
http://www.explorerforum.com/forums/showthread.php?t=322427
If it is indeed your ABS module whirring, the strange battery issues can certainly cause it to do funny things to the pump, which I can imagine might make a whirring noise.
The only good, thorough way to test a battery is to charge it some (which takes very little time on a lead-acid battery) if needed (which apparently, at 83%, yours doesn't), and then test it under a large load, ideally somewhere in the range of 200+ amperes (more than that is supplied to the ignition motor), and the power supplied should be measured with a computer (nowadays handheld, but 20 year old ones exist the size of a small tool rack) to see if it is relatively stable. It should then be charged again to make sure it holds a charge properly, and tested one more time. This takes a good deal longer than 10-15 seconds, however. If Dobbs isn't doing this, then they're not being thorough. AAA will do all of this in your parking lot with a hand-held computer for you and also monitor for a power leech (i.e. short circuit) if you have it. If AAA can do all that in your parking lot, it's pretty bad if Dobbs is only doing a volt test in their store/shop, but also fairly common - even licensed mechanics make this mistake and replace alternators, etc. before even trying it.
Failing that they should at the VERY LEAST be testing the voltage drop under load. When you are drawing significant current the voltage should drop. Ask them 'how many amps or watts are you drawing and how much does the voltage drop?'
Irrelevant technical details: P = Watts, I = current in Amperes, V = Voltage, R = Resistance (caused by a load of some sort). P = I * V, and V = I * R; you can derive from this things like P = I * I * V * R. When you test, you use a certain resistance (load) and voltage. Thus, you could use a very large voltage (say, 120) and draw a lot less amps I, but get the same wattage, if you use a different load. In the end you really want to know that the battery can supply the correct amperage with a 12V draw though since that's what the starter takes (note: a large continuous load will reduce the voltage across the terminals down from 12V while it is being drawn, the test is only to see if it can sustain such a large draw without too huge of a drop).
Back on topic now.
If they don't test under load, it doesn't mean they're shady, just that they have poor procedures or employees (I have no idea what a Dobbs is).
If you'd like to know how much of a load is being placed on the battery by (potentially) the ABS pump/module or whatever is whirring while your car is off, you can test it yourself with the right cheap equipment, but I forget how. Sorry.
