The oxy is building pressure in the system. Don't tighten the jug cap; leave it unscrewed to vent the pressure. And the Multi-Sprayer draws better with the jug cap unscrewed.
Try adding 2oz. delimonine / citrus solvent to the 2 gal. jug to calm the oxy volcano. It doesn't reduce the cleaning action of the oxy.
Your a funny man Chavez. The guys hit it the first time. It isn't the pump it is the pressure from the H2O2 loosen the cap and see if that stops it. Also the gun might need replacing as it isn't holding back the pressure which it should as that isn't that much pressure but it isn't the pump. The gun is $49. Reminds me I need to get the multi-sprayer stuff on the website.