So I'm afraid I either have some detonation or "knock" in my new engine in my 89 2500 burb 350 TBI.

Sometimes...usually shortly after I start the truck when I'm accelerating up an incline (where more torque is on the engine) I get a sound that sounds like my radiator fan is whacking into my fan shroud. I thought the extra torque was "tilting" the engine and the fan was running into something.

But when I had my finace sit in the truck with and hit the gas and the brakes at the same to time to make the noise...the noise happened, but the fan wasn't hitting anything! It sounded more like it was coming from the engine. Only happens under load, starting from a stop un a hill etc.

The other thing I noticed was it seems to go away once the truck warmed up.

This makes me nervous. I'm not sure why my engine would be detonating unless the distributor is shot or was slipping??? But what is "engine" or "rod" knock....I've heard it used all the time but I guess I've never stopped to know for sure what it is?

Am I experiencing detonation? Or rod knock? What should I do about it?