ASEMaster6371 is right. Since the '87 model year GM has had a real poor generator design. They develop huge voltage spikes that can destroy the internal voltage regulator and diodes, induce spikes into computer sensor wires, and, . . . and, . . . show up as static on AM radio stations. When you hear it through a cassette or cd player, the spikes are coming in on the power wires.
It is real common to go through four to six GM generators in the life of the car. The way to reduce the number of repeat failures is to replace the perfectly good battery at the same time unless it's less than about two years old. As they age, they lose their ability to dampen and absorb those spikes. The old battery will work fine in an '86 or older car with the better generator.
The excessive whine in the speakers suggests your generator already has a defective diode. That will reduce the output capacity to one third of the unit's rating, and "ripple" will be very high. That ripple will also cause a whine in the speakers. Here's a better description of ripple at the bottom of the page:
Before you spend any more money to cover up the noise, have a load test performed on the charging system to see if that is causing it. The typical generator should produce around 90 amps or more. If the test finds closer to 30 amps max, it will show high ripple too. Professional testers show ripple not as a voltage but as high or low on a bar graph.
If you need a new generator, don't waste your money on one with higher output. That will do nothing to reduce noise. It is very rare to need the full generator output. It will deliver exactly as much current as is needed by the electrical system regardless of its maximum capacity.
Monday, June 4th, 2012 AT 8:15 AM