2014 Cummins ISX in a Freightliner whistle at idle and raising RPMs about 100-200?

New to me Freightliner with Cummins ISX. Today when driving I noticed it when coming down to an idle at a stop or letting off the throttle all the way I would hear a whistle coming from the turbo(I assume) that I hadn't heard before. And when you put it in neutral and have the parking brake on the RPMs go up about 100-200 and you hear the whistle. Shut it down and started it back up and it idled and sounded normal for maybe 10-15 seconds and then it bumped the RPMs and the whistle came back.

Any ideas? Thanks!!

 

Thanks for the reply I will check. Any reason the RPMs would go up at idle when it does that? RPMs at idle are usually 600 and it doesn't do it then. But now it idles at 700-800 and makes the whistle.

But on startup the truck idles where it is set at 600 and then quickly it jumps up 700-800 and makes the whistle.

 

That was also a thought but no regen lights or anything came on. Had a 2012 Freightliner with the DD15 before this and if it did a regen parking break had to be set and the RPMs went higher. But this is a different motor and different year.