I have a 2012 4.0, the noise is Very likely the timing chain wear guides and chains that Nissan swears have been fixed in production prior to 2012. I have spoken in person to at least one owner of a 2013, 2014 and 2015 4.0
Frontier that currently have the timing chain guide problem. I to have the problem on my truck. Since this defect is not a "Safety problem" Nissan is not required nor motivated to issue a recall. The more serious associated issue is the aluminum flakes that get dispersed in the oil, that damage bearing journals, oil pump and start wearing everything else in the motor. Next oil change look at your oil in the bright sunlight, if you see reflective flakes and glitter in the oil, you most likely have the problem in your motor. The flecks will be non-Ferris, (not attracted to a magnet). Have the oil tested by Blackstone, that will tell you exactly what is going on and required to even begin to have a discussion with Nissan or a Nisan dealer. I have 50K miles on my motor now, in speaking with Nissan it is clear Nissan has no intention of addressing this problem for my truck even with full documentation of oil change history and oil tests from new.
You may also notice a knock in the motor at light acceleration around 2K rpm in cold weather, temps below 50 degrees that is louder the colder the outside temp. The knock can dissipate when the engine gets to full heat soak, not water temp.
Options are sell the truck and taking the financial hit. Keep driving it knowing the motor will get worse and need to be completely replaced not rebuilt. Nissan has been very clear that they will offer no action under warranty to address an aspect of the problem for my motor. Best case if Nissan took any action it would be to replace the outer timing chain and the lower gear and guides. They will not replace the upper cam gears that actuate the variable valve timing, they are just under $500 each! Needless to say I will not purchase a Nissan product next time. Nissan has burned me twice with defective internal engine parts on two vehicles and that is enough for me.
Get your oil tested to start the investigation. Do not listen to all the internet experts and speculate, it is a waste of time and offers not value. Deal in facts only, no emtion with Nissan, they do not care, it is all about the money / business, nothing personal. Get the oil test and deal in facts only. Good luck with your journey. - DH99