98 S70 Engine ‘singing’ noise [broken vaccum hose at air cleaner box] Topic is solved

Stu70 · Post by **Stu70** » 05 Jul 2019, 18:22

Hello, I’m hoping someone can shed some light on my troubles...
B5252 10v , once car gets to operating temp to begins to “sing” I’m devaluing Volvo’s when I pull up to lights- it’s a ‘oh he should get that noise fixed’ sort of noise - see video
PCV done 35k miles ago. Noise started before I did timing belt, pump and tensioners, and keeps going when serp belt off , but stops when engine revved -see video.
Using an electronic stethoscope, it seems to be coming from block or PCV tank. Louder down the gap between 2-3 intakes on the manifold.
Any thoughts ? getting parts from across the world does make it expensive to ‘shotgun service’- just replace everything it might be and never knowing what it was that cured it.
I’m wondering if a partially blocked hose might set up a resonance? Or a hole in the intake gasket/ manifold might whistle?

Video here...

Many thanks

Post by **abscate** » 06 Jul 2019, 04:01

That sounds like a vacuum leak, I would pull the intake and check the Pcv system for a loose or holed hose

Stu70 · Post by **Stu70** » 03 Aug 2019, 00:34

During reassembly of the inlet manifold not really finding any thing out of order. Last thing to connect were the hard hoses on the back of the air box , putting more pressure on the hoses than when I tested them with a tug. I found the top hose that goes to the hot air bypass flap had cracked and was just holding on by a thread, right down low on top of the vacuum damper.
That would explain the high pitched whine and it only happening when the car was warmed up.
Thanks Abscate for your reply, and your thread on tactile vacuum hose checks. Had I throughly tugged and looked properly even right down there I could have saved a few hours and few dollars...

Post by **abscate** » 03 Aug 2019, 06:53

Stu, thanks from the follow report from NZ!