Hi there,

My engine do an up and down noise, any idea?

 

Up and down noise... You mean the noise gets louder and quieter?

Any CEL/codes? Does turning AC on/off make any difference?

 

Yep exactly

The noise get louder with higher RPM, but not faster. After 2000 rpm, its hard to hear it

No CEL code

 

It almost sounds like a clutch pulley or bearing is bad but hard to tell unless I hear it in person.

 

I found a video with this exact same sound and its about the alternator. Me, my friend and the mechanic guy tell the same, its probably the alternator. I put a metal bar on it to listen and it seem to come from here

is350 2018 seem to have 2 alternator versions, one with 6 grooves(angle bracket) and one with 7 grooves(straight bracket). Mine seem to use the 6 grooves one. But how the **** the 7 grooves can cost 350$ and the 6 one 750$?!! The only difference is the grooves and the bracket. The power output is exactly the same, 150a

What I can do to reduce the cost?

 

I finally found one on rockauto for 360$ CA shipped! Refurbished from BBB Industries. Someone here have experience with this brand?

 

maybe take the belt off and see if they pull has a lot of play.