So about a week ago I noticed the famous Volvo squeal on my 2005 s80 2.5t and after some research I concluded that the pcv breather was bad. I changed the pcv and I still had the white smoke in the oil cap and dipstick and squeal. Then after more reading I realized that I didn't clean the PTC valve. So I went back in to rebuild the whole system and clean everything out. I confirmed that everything was assembled correctly and I put it all back together. I took it on a test drive around ten miles. I got home and did the glove test and it got sucked in. So I turned off the car and got ready to go inside the house and call it a day. Then I realized that the car wasn't parked straight on the curb so I went to repark and I heard the squeal noise. I was tired and it was late at night so I just went inside and now I'm here. I have around 130k miles and I need some help. Any help will be greatly appreciated thanks in advance.

 

It happened with me, there is nothing to be worried about unless you broke any air hose. Check again all the Air hoses specially the one coming from Intake to PTC Valve, in my case Intake small air hose was lose a bit so reattached firmly and whistle sound gone.