I could use some help. I have a 2000 explorer 4wd XLT. I hear a clicking or knocking noise seemingly from the oil pan. This only occurs however, when I put the vehicle in gear. It will completely disapear if I put the truck in park or neutral. The noise seems to follow rpm's, again only if the truck is in gear. A local mechanic wants to charge me $650.00 to take off the oil pan. OUCH! Of course he doesn't know thats where the problem is. The truck has 80,000 miles almost all highway. Oil changed every 3000 miles. I did switch to synthetic at about 75000 Could that be a problem? Please Help. I would appreciat any input.