My '99 Miata has been making a shrieking noise if the engine is warm and revs fall below 1000 RPM . If I accelerate to 3000 or so RPM--usually in3rd gear, drop the clutch and let the revs fall back, it goes away. Belt dressing has helped. It may be related to generator belt. I had it replaced about 6 months ago after it shredded, but the noise did not develop until 1 mo. later. When I drop revs, lights dim a bit. Other threads and maybe shop manual indicate possible problem with the clutch--big $$$. But could it be the belt itself, or a shaft of whatever is connected? Anyone have a similar experience?