HAS ANYONE WITH A 2001 XE 4X2 3.3V6 HAD A PROBLEM WITH ENGINE KNOCKING WHEN THEY USED MOBIL1 SYTHETIC OIL. I LIVE IN FL AND WITH THE HEAT I FIGURED I TRY SYNTHETICS. MY X ONLY HAS 21000 MILES AND IT'S KNOCKING. I SWITCHED BACK TO A STANDARD OIL, AND THEKNOCK WENT AWAY. I'M STUMPED. SUGESTIONS ANYBODY