In the past when I have had a bad alternator bearing (on other cars) the screwdriver test has revealed a LOUD sound. If you have squeaking this could be the belt. One test is spray a little water on the moving belt with a plant sprayer (be safe, keep your self away from the belt!!). Spray it on one side then the other and see if the sound goes away for a short time. Old belts will squeak. I have already changed the belt on my C230 for that reason.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra