Strange noise from N55

[dicker]

Hey guys, my N55 is making a weird noise at idle but it comes and goes, almost like it's something the engine is doing since it comes and goes on a pattern. The problem is it sounds like an awful knocking noise.

It's got 16k miles and it isn't throwing any codes, tailpipes do look a little whitish though (I've heard this is common from N55's)

Here is a video I took of the idle, sorry you can't see anything, it was dark outside.