yeah rod knock is when the bearings on the rods start wearing down due to either a lack of oil or a lack of changing the oil. Basically the bearings end up knocking against the crank and cause that rattling sound your hearing. What you can do to test it and verify that it is in fact rod knock is start unplugging the plug wires a cylinder at a time and revving the motor up. If the sound stops once you remove the wire thats the cylinder with the knock. Hopefully that isnt what it is though. If the knock is mild you may get away with just replacing the bearings and be ok, but once it gets bad you will either have to rebuild the motor or replace it with a jdm motor or something equivalent.
Mine started out very quiet, lasted about 1000 miles before it got really bad and I didnt feel comfortable driving it. It probably would have lasted longer but I was pushing the car on the hwy (for probably about .5mile, my house is only 3 exits down from where i work) and by the time I got off the highway and stopped at the light the car cut off. I cranked it back up, but it was knocking like a bitch. I ended up getting the car towed to my house and havent driven it since. Long story short, just make sure you are VERY gentle with the car until you discover the cause of the noise.