if they were non-polar they were most likely audio coupling caps.
that would seem to indicate that you have dc offset problems somewhere in your audio path as they should have little dc across them. It could also be some odd power supply issue causing dc offset, not likely.
are the caps bulging? if so that indicates overvoltage or internal heat damage, not usually caused by external heat. External heat damage usually is drying of the electrolyte and loss of capacitance, not bulging.
Replacing non-polar caps with polar caps may die early because you get the wrong polarity installation! oops. Reverse polarity on caps will cause early failure and bulging or worse is often part of the failure symptom(s).
Alan
