I've read up on knocking, haven't seen any post that matched very well...

My 04 350 6spd has 87k miles, always has run very quietly and smoothly with very little oil consumption. Never abused, very rarely redlined.
But today, I started it as normal and immediately a rythmic, knocking noise emanates loudly from the engine, with a rough idle. The noise is consistent with the rpm of the motor (1 revolution=1 knock). The knock is constant throughout the rev range, though it quiets in particular places.
Rough idle smooths out after 10 seconds, knocking continues.
Allowed it to idle until normal engine temp, knocking subsided a great deal, but is still there.. motor running totally smooth aside from the light knock.
Oil was not low,outside temp about 60 degrees. I'm afraid to drive the thing now. The motor has never acted up in 8 years of ownership.
On moderrn motors, I have no idea where to start- What are ya'lls thoughts?

 

Bent rod?

 

easiest is check the serp belt, if its badly worn or off a little it emulates rod knock

 

I don't know why, but knocking has totally stopped now, and car runs like nothing happened. Still wonder what happened though.

 

Thanks for the sugg. Knock stopped completely, motor runs quietly. I have no idea what happened.