Lights flickering & car stalling
 

I have a 1996 Monte Carlo Z34

Alright let's see if I can explain this well enough to be understood without actually seeing what's happening. I'll start this off by mentioning the battery, and starter are brand new, and I have bypassed my security system when it decided to crap the bed on me and leave my car stranded at my work parking lot for a month before I finally figured out what the problem was (which is why I have a new battery and starter, also a new neutral safety switch, the one on the transmission, not the one under the dash).

The car will start just fine (most of the time) even after sitting for more than 3 days without running.
The other day I got to work and rolled up my window, while in park, and the RPM gauge jumped from 1 to 5, but no revving of the engine happened while I did this. Also while rolling up the window the headlights would dim, and if I did this long enough or in rapid succession then the car would stall. I did this same thing with my multimeter connected and battery and alternator are checking out fine.
My dash lights flicker quite rapidly sometimes, but not all the time.
I also get a high pitch buzz/hum coming through my speakers when the flickering happens, but is mostly noticeable when I have the tape deck converter inserted into the tape deck. Regular radio stations either the noise is very faint or not audible at all.

Today I got the car running, drove down the street and all of a sudden the car just stopped running, so I had to coast as I pulled over to the side of the road. I put the car in park and turned the car off, then turned the key and it started up like there was no issue at all.

I just bought a multimeter to test the battery and alternator and they both checked out fine; 12.7 when car is off, 14.5 when car was running.

Is this a ground wire issue somewhere in the car? If so, any suggestions as to where I should start, and how to test the ground wire if it's any good?

If it's not a ground issue, what else could it be?

I'm hoping this makes sense, and I'm hoping someone can steer me in the right direction.

If you haven't figured it out yet. I'd check ur vacuum lines from the intake for ur engine problem, assuming the alternator belt is tight. And that sound has to do with insulation of the speaker wires and the point of ground.