Fretting hand....(you need to be playing through your amp for this). Just spend 10-20 minutes putting gradual fretting pressure with fretting hand and hear when notes play/sound cleanly. Start with no or very little pressure and add pressure until note sounds. This is all the fretting pressure you need...any more is wasting muscle energy and may cause fatigue and badly intonated notes. The thing is to be constantly aware of this (minimal fretting pressure) when playing. Unfortunately, when people start concentrating on what they are doing with their non fretting hand that the fretting technique goes pearshape and they start to overpress again.