Clacking under load?

[JHZR2]

When I had my 240 on the interstate the other night, I found a strange thing. First off (this isnt the strange thing, it has always done this) the engine shakes at idle like a tractor, but the slightest bit of extra rpms and it is smooth as glass. It has plenty of pep and takes acceleration without an issue. It's happy cruising at 65-70 all day.

But the other night I was cruising at about 65mph, very little throttle, and heard a distinct clatter (or nail?) very sporadically, and very lightly. But it is a sound that stands out. It's intermittent nature puzzles me though. Like on flat terrain, cruise on or off, constant speed and throttle, it would occur a few noises maybe every 10sec.

I did post on a wet injector... At 75k am I really due for a rebuild of the injectors???