Whining, stalling and flickering (unabridged)

My 2001 2dr 2wd Blazer needs help. It has 45k miles on it, and I have owned it for six months. It has the 4.3L vortec engine, by the way.

Up until a few days ago I had been ignoring a whining sound coming from (or so it would seem) the middle of the dashboard directly behind the stereo for the past three months. Everything was running okay, so I just turned up the radio to "fix" the problem.

The noise seemed as if it were coming from the radio itself, except I would hear it when the unit was turned off. The best way to describe the sound is to liken it to a siren, and it would increase in pitch along with the engine's RPMs. The sound wasn't affected by the electrical load, only engine speed; it even changed pitch as I shifted gears.

Over the last few weeks I noticed that some of the instrument lights would flicker when I was stopped at a red light. Most notably affected were the gear indicator (P R N D 1 2) and radio display. However, this flickering would go away almost completely when driving at highway speeds or thereabouts. I would also notice my headlights quickly flash off and back on during accelleration. The headlights would do this once or twice on my way home from work, usually in the first five minutes of my drive.

Since the truck felt like it was running okay despite these things, I considered them petty annoyances and tried not to think about it. Several days ago that changed. After work one night I had to try three times before the engine would start, and after it did I had to rev it up a bit to keep it from dying. At the first stoplight I came to I had to shift into neutral and keep my foot on the gas to keep it from dying, but after 10 minutes of driving on the interstate it returned to normal operation.

The very next morning I started it up to run some errands and encountered the same thing as the night before, except the problem didn't go away after a few minutes of driving. The engine stalled at 50mph when I took my foot off of the accellerator to coast to a stop at a redlight, so I veered into a parking lot and ran it in neutral at 2k RPMs for five minutes to see if the problem would clear up. No dice.

I wound up driving the mile back home with one foot on the brake and the other on the accellerator, and it died a few feet short of my driveway.

My conclusion was a faulty alternator, so I bought a new one at NAPA and installed it that afternoon. After the new alternator was installed, the truck initially behaved like it had before: stalling in idle, engine sounding smooth at higher RPMs.

But after a few minutes of running the engine, everything suddenly seemed perfect. No more flickering dashboard lights, no more sound, smooth idle without any encouragement from my right foot. I drove it around for 30 minutes and was elated to have fixed the problem. I took it out several more times that afternoon, and everything was fine.

The one thing that caught my attention, however, was that the voltmeter(?) on the instrument panel showed my battery steadily losing power, instead of charging up as I had assumed it would. The very next morning the battery warning light (charging system) came on, and a stop at NAPA revealed that the new alternator was pushing zero current and the truck was running exclusively off of my ever-dwindling battery power.

My first question (if any of you bothered to read this far) is whether I was wrong to originally assume a faulty alternator. Secondly, I had a rough time getting the new alternator to seat, so I used a rubber mallet to get it into position. Can an alternator be damaged/destroyed by pounding it into place in this manner?

Also, if I was wrong about the problems stemming from the alternator, why would they all go away when the truck was just running off of the battery? The old alternator squeaked when I turned it by hand after removal, and I naturally assumed that was the noise I had been hearing for so long.

My thinking at this point is that I should get another alternator and install it without using a mallet this time, and see if that fixes the problem. Am I focused too much on the alternator and ignoring other things that could be to blame, or am I on the right track and just need to do a better job of executing this next installation?

Any suggestions would be greatly appreciated. Sorry for the huge post, but I wanted to make sure all pertinent information was included. Thanks!!!

I would assume also that your alternator was bad if when you took it off it felt rough when turning the pully. Have you checked your battery. It may just be dead or slowly dying. You could have damaged the alternator by hitting it but its hard to tell. If another alternator fixes it them that may be it. If not I would put in a new battery. Good Luck