Weird chirping noise, tach needle flickers

[tiggs]

Ok, so here's what's happening: 93 240sx Hatch with a 95KADE

Last friday I started hearing this small chirping noise between 3500-4500 rpm. Unfortunately I didn't have any time all weekend to pop the hood and take a look. Since then I've had to drive the car around 200-250miles. As of now, the chirping noise starts at around 1700rpm and continues to the rev limit. It's a very annoying noise. It doesn't sound like a belt, my of like an unballanced pulley? Like it's rubbing or something.. I dunno...

Now at the same time this started, my tach decided to start being funny. At the same 3500rpm the tach would flicker up to around 4000rpm. Like a nervous twitch. As of today, it will flicker anywhere in the range that the chirping happens. I'm guessing these haveta be related.

I'm trying to narrow down what might be wrong. I wont have time to pop the hood until this evening (I really need a second person there to rev the engine so I can try and fine the location of the chirp) so I wanted to see if you guys had any ideas on what I should be looking into when I finally get the chance to check it out. I'm going to try and get a sound clip tonight, maybe a short vid to show how bad the tach flickers.

Does the tach signal come from the alternator? I know in some cars it does but I don't know about ours.

Thanks for any help you can give. If you frequent other 240sx boards you'll probably see this thread in there as well, lol.