metalic sound from engine

[lincolnmatthews]

Did a search, thought I had read, but could not find it, regarding a hollow, metalic sound coming from my 83CD engine when driving usually between 40-60mph. Seems to be more pronounced at a steady speed, if I let up on the throttle, or push on it a bit, then it goes away untill it evens out again. I do not remember this being around a year ago or so. It has come on very gradually?. It is not loud, just somewhat annoying, def. not a vibration, any thoughts, anybody else experience this?. Car has about 230000 miles, could be just normal wearing, thanks for any input.

On another matter, sorry for the 2nd ques. & post length, went to look at another 83D turbo last night for a friend who wants to buy one. Car had about 210000 miles but was a total "dog" off the line untill it got over 2000RPM. then it came alive. It appeared to have alot of blowby, they have been running biodiesel in it for about a year. We checked with the local diesel pump rebuilder, (very good reputation), he said stay away because of the biodiesel, he said it will def. ruin the pumps, with a rebuild being about $1000, any opinions on this?? I know alot of you guys are running bio?, thanks again for any help, (did not do a search on this),