that takes me back to my old RST, there will defo be a hole sumwhere on the hoses with that hissing and it'l be in the most fookin annoyin place possible (always is)....

have you got two fans running constant? as much as most people hate them when i fitted bonnet raisers to me old 1 airflow was seriously improved and i did notice a difference. worth a try maybe??

long shot but you might have an airlock....