Check the 4 Pineer speakers. take the sub out and see if you still get the
distorted. Cd offers better signals particularly when it is recorded above
48k. Did or are the mids crossed, maybe just needs to be adjusted. If you
can control the frequency set it to about 500 hz and see if the distortion
goes away. Then you can just play with the range till you find a safe level.
Full range may cause them to distort some. The FM modulator maybe a factor
depending on which one. ChystalLines - shouldn't be a problem