OK RC, it was late.
2:1 or 3:1 are just about as bad. 2.35:1, 3.35:1 or some odd setting is beter.
The belt drive needs to slowly "walk" around the gears and not have the same spot match up every 2 or 3 turns.
If you have to run even ratios do it with an odd tooth gear and an even toothed gear. Don't use two gears with even teeth counts