Lifter problems????

It also sounds like you got a lazy lifter and it's cropped up now that you've gone to a lighter (viscosity wise) oil. You can try to find the bad lifter but I caution you it can be dangerous if not done properly. Pull the valve cover off the site of the engine that rattles. Make a tin shield the length of the head and about 6 inches tall for keeping the oil in the head and not splashing on the hot exhaust. Have a bucket of water near by just in case. Now start the engine and using the end of a hammer handle, wood end, push down on each rocker arm directly above where the push rod seats. You should hear a tapping sound as the lifter collapses and when you remove the hammer handle the tapping should immediately go away. If the tapping sound takes more than 5 seconds to go away the lifter is bad. Be sure to check all the rockers on the head. This isn't easy to do especially with a high lift cam but I've had success with it. But what ever you do make sure the oil is not getting past the shield and running down the side of the block. :evil2: