As you stated start with pulleys and tensioners. Start the car with no belt and see if the noise is there ( i think you will need a scanner to delete the faults after doing this)

 

belt is not even on the pulley/rollers....half on and half off?
put a couple of washers on the pulley shaft to bring it out so belt is even

 

Happy Holidays!

As you can hear from the video, the engine is making "dang dang" noise recently. I'm not sure what is going on, maybe I have a bad pulley or tensioner?
The drive belt is brand new, I replaced it because it used to make squeaking noise.
Occasionally, while idling or in traffic, the RPM would drop down for seconds before pulling back on and it's like having a sudden rapid short breath.
Does anyone know what's the problem?
Thank you!

Maybe you can confirm...

But from video it sounds and looks like the noise happens every time the white mark on the passes. Is the noise definatly in time with the belt?

If this is the case definatly a belt issue

 

Thanks guys!
I will replace the pulley and tensioner later this week.
I will keep you all posted.
Thank you!