[Blas]

I agree, the buzzer is most likely the low brake fluid warning sound, that is the only buzzer standard on the car. Acceleration can change the level of the fluid in the resevoir causing the warning buzzer to sound. Usually means the fluid is low Careful which brake fluid you add.
The DOT 2 spec is for drum brakes and is obsolete. Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid. That leaves DOT 3 and DOT 4 fluids. These fluids are compatible with each other and may be interchanged or mixed with no ill effect

As to the eratic tach operation, I also agree with the ground suggestion, check the variois grounding locations unser the dash. There is a large cluster of brown ground wires at the center of the dash near the accessory plug (if you have one fitted - they were options back then) look near the top of the 2 support bars up to the dash. Send me an email (see below) and I'll send you a photo of the grounds in that area...Always glad to help.
FYI: (BROWN wires are always grounds on SPF's, even BROWN with color stripes)(RED and GREEN wires are always power)

STL Mark..
Yes #126 is an early version of the Superformance product, probably built about 1996 or 1997. Very similar to the latests cars, but different brakes and wheels, dropped floor configuration, cowl height, early wiring harness etc. I have a link to a webpage with the changes listed in the build configuration somewhere...I'll try and locate it.