Fix the noise source first — a gate treats symptoms. Bad cables and ground loops need to be solved.
- Threshold too high — gate opens and closes mid-sustain, chopping off your notes. Especially obvious on slow doom chords. Lower the threshold until it only closes during actual silence.
- Release too fast — tail of each note gets cut abruptly. Sounds mechanical. Set release slow enough that the gate trails off naturally.
- Attack too slow — gate takes too long to open, clipping the pick attack at the start of each note. Should be nearly instant for guitar.
- Gating a noisy amp instead of fixing the noise — a gate treats the symptom. Bad cables, single-coils near transformers, ground loops: fix the source first, then use a gate for what remains.
- Gate before distortion — some rigs benefit from a gate in the FX loop (after gain) instead of before the amp. Distortion amplifies noise; gating after the gain stage catches this.