I noticed this sorta knocking noise in my wagon a few weeks ago... I kept driving it like normal. Since then I've driven about 800 miles with no problems and I don't think the noise has gotten any louder?

Description of the noise:
-Kind of a low pitch-ish knock, not super metalic? Almost like an iddling dirtbike, except not as "poppy"
-most noticeable at 1000-1250rpm but still sorta noticable untill 2000rpm, pretty much becomes silent after 2000rpm, the engine revs up smooth?
-to make the noise the loudest I let it drop to 800rpm then i sorta rev it just enough to get it to about 1200rpm
-if I hold it at about 1100 the noise almost seems to skip every now and again, sorta like an iddling dirtbike like I was saying

Does this sound like a knock?

THANKS!

 

Please help!

Also I should mention that it's almost silent when cold, and gets louder

-another thing is there's no metal shavings in the oil?

 

..