The point was made that if both PRVs are supplying water at the same pressure then system should work OK, I would think that you could have at least 0.5bar difference in the two and still have proper mixing but I would agree though and can't really understand why it wasn't done the "proper" way, I Iinclude a schematic once again which is quite clear, the EV is also wrongly installed so all these might conspire to cause noise in a paper thin unvented cylinder.