Autotek Issues

Hi the amp is an Autotek 7300 BTS

Issue is the sound is distorted and bitty at low volume, when the vol is increased the sound is clear.

I have cleaned the gain, bass and treble pots and crossover switch with contact cleaner and no change.

The power supply capacitors were leaking so I replaced them - no change

I also replaced all the capcitors in the audio section, sill no change.

All the output transistors checked out fine too.

The amp doesn't overheat, or cut out, at high volume it sounds good, just distorting at low to mid volume?

what could be the issue?

thanks in advance