Speaker-Eating dashboard?

If the one side is failing, swap the good and bad speakers. does the
bad speaker become good? and the good speaker turn bad? is the stereo
properly grounded?

you sure about that? it's true that distortion tears up speakers, and an
underpowered amp can lead people to crank the volume up beyond clipping,
but i've never heard it suggested that the amp be rated for more power
than the speakers.

You need more power. A good rule of thumb is that the amp should be
rated at 2 times the speaker rating. This prevents clipping which
speakers apaprt.

Hachiroku wrote:

50W continuous? I have some 2' tall floor speakers rated for 50W
music power but only 1W continous (instructions said not to exceed 8V,
peak-to-peak, for more than 2-3 minutes).

If you don't blast them at high power all day, about the only
electrical thing that usually ruins speakers in a hurry is DC from the
amplifier. Switch a digital voltage meter to read DC volts and see if
there's more than about 0.1Vdc across the amp terminals (an analog
meter won't work for this). Don't measure to chassis ground because I
think that most car stereos now use two floating outputs (an easy way
to get higher power without higher power supply voltage).

Have you tried pressing the speaker cone to see that it moves in and
out without binding? Some of my Ford factory speakers (base audio
system) that scraped the magnet when moved also buzzed, but I had a
Ford radio cause a buzz because of some power supply problem (I think
it was the power supply that drove the LCD).

Find a cheap speaker, hook if up electrically but don't install it
physically. Just extend the wires and leave it somewhere in the car to
figure out whether it is related to the physical installation or a short
from the radio.

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