Quick answer
Harsh or clipped output at moderate volume is almost always gain set too high for your headunit's output. Start at minimum gain, set a sensible headunit test level, then raise the gain only until distortion is barely audible. Back it off slightly and repeat per channel if you need to.
Problem
- You're setting your amplifier gains without clipping the speakers.
Symptoms
- Distortion only at high volume.
- Your amp's clip LEDs flash.
Cause
- Your gain is set beyond the clean headroom for your headunit's output voltage at real listening levels.
- Charging system voltage sags at the amplifier under headlights, fans or winch load.
Fix Step-by-step
- Set your amp gain to minimum.
- Set your headunit volume to a sensible test level with a clean test tone or a known track.
- Raise the gain until just before you hear distortion, then back it off slightly.
- Repeat per channel if your gains are independent.