Awl--
Is it usually the amp/transistors, or the speaker(s) itself? Both rear-seat dash "woofers" (mounted vertically, behind the headrests) buzz at any kind of volume, sound real crappy. Happened some time ago playing Creedence in my garage.... :( Radio: Panasonic 1263, from 1990 Mazda 929S, 6 speaker, w/ equalizer. Pretty nice.
Also, these two speakers have their own plug to the back of the radio. Does that imply that they are powered separately with a crossover in the radio (ie, only the lower frequencies being fed), or are all six speakers powered the same?
I can't find the manual (or the radio on the web), so any guesses as to what a stock decent 1990 radio put out, in watts per speaker? 4 ohm.