The heatsinks on the CA300 ring like a chime. Try to dampen the fins. When I had this amp, I used some thick mdf wood panels and brass weights across the top of the fins to damp out the ringing. This cleaned up the sound to a remarkable degree. There are likely more elegant solutions available. BTW the DR8's didn't exhibit the ringing fins. Of note, the transistors are mounted to the back plate of the offending fins hence the degradation caused by the ringing.
