there is a strange "diesel" noise coming from around the middle of the head on my '99 5sfe camry,i have tried putting in thicker oil it seem to have made it a little bit quiter but i am concerned of its longevity ,engine still goes beautifully,revs nicely, but at idle this noise is quite apparent,i was told by some mechanic that it could be the exhuast cam tensioner spring wearing,has somebody come across this noise,and if so how to fix it,cheers scott.