Damn.
Yes, that's the right way to start a thread in this case. I built a mild 350 a year ago (about 300 HP, in a G20 van), drove it for 5000 miles and a couple of days ago, suddenly, there's a wierd sort of clanking noise coming from inside the engine. I'm almost certain: something's loose What could that be? What would it sound like if a rod-cap had come loose, but not off completely? Since I noticed it for the first time I might have don 5 miles or so, it's getting worse. It sounds like a sort of loud mechanical rattle, which is pretty consistent with engine speed. Sounds horrible. No, it's not the fan, TC bolts or engine mounts. That's what I checked first of course...
Yes, I do like to step on it and spin tyres and the sort. And yes, it is a 2.5 ton truck and yes I do do 90 mph on the highway and yes, I am running stock rods, caps, and bolts

Any help or ideas to what the rattling could be woudl be really appreciated!

Madmax


For info:
350 bored +.060, 4 bolt 010 block
sealed power flat top pistons
491 heads (64cc)
roller comp cam kit for high torque
stock crank (.010 under)
stock rods
600 Edelbrock carb
performer intake
until now troublefree, excellent performance, all spark plugs clean and dry, ignition in good order (the sound's NOT a ping)