The first and most worrisome to me is the obvious knocking coming from the rear 3 cylinders area (it's most evident in the last 5 seconds of the video). Is this bad? Is it just harmless valve chatter or something serious? (The car is fully warmed up for the video)... Oh, and I don't know if it is related, but I just barely got a P0507 (high idle) code... GAH! What's going on?

The second is that high pitched whining sound from the starter/tranny area. Is it the transmission? (its a 4AT)

 

It's hard to tell if it's just poor video, but sounds like it's hunting?
Are the revs fluctuating?

Doesn't sound good brother how many KM? And did it just start out of no where?

 

I don't think it's hunting... I was slightly revving the engine to make the 'knock' sound more apparent. It's just a slight knocking but definitely noticeable... Started out of nowhere as did the code it threw for high idle. Car has 229K kilometers (142K miles).

 

Try a read through this thread it is old but may be relevant because of your P0507 code
http://forums.maxima.org/5th-generat...gh-solved.html

Read this thread on the idle air relearn especially post number #15 as it mentions your code
http://forums.maxima.org/5th-generat...need-help.html

As for the knocking, the obvious things would be low oil, carbon build up you can do as I am at the moment which is running Auto-RX in my oil crank case for the duration of one oil change cycle ... seems to have quieted my knock completely. http://www.auto-rx.com/ the product can be used for both cleaning the engine internals as well as there is an application for the tranny.

Just a couple of options

 

Wait, so you didn't take the vid, you were in the car feathering the throttle?

If it's not hunting, you have to do some isolation. By the rear 3 I assume you mean closest to the firewall (right bank [1,3,5]) ?

I can't tell from that video bro, so do the following, make a better vid (sound), longer without any throttle feathering if you can.

Is the knock constant or intermittent?
(this will tell you if it's a single cylinder or a bank)

Top end issue is a slower sound, bottom end is quicker. (camshafts rotate at half the crank speed)

Also, Isolate the cylinder/sound with a stethoscope.

Ghost posted great links for you as well.
I suspect a possible intake leak.