Low flame when all burners on

Question

ever since I have had the grill, when I light it using the ignition burner i get full flame on THAT burner only. When I try to light another burner the flame level drops. with each additional burner I light, the flame level drops. I have only been able to get full flame on all burners twice since I have had it. When I get it to work with full flame, the regulator makes a rattlling sound. I have swapped the regulator and and bottle twice. Still no luck!