I HAVE TO REPLACE MY 3RD CATALYTIC CONVERTER (DUAL CAT SYSTEM) EACH TIME THE SUBSTRATE IS LOOSE, RATTLING AROUND...THE FIRST TWO (ORIG. EQUIP.) LASTED 150,000 MILES BUT NOW ONE REPLACEMENT IS BAD AFTER 5,000 MILES, ITS RATTLING...DID I GET A DEFECTIVE ONE OR IS THIS INDICATE A FUEL MIXTURE PROBLEM? HAS ANYONE ELSE HAD THIS PROBLEM?