Can anyone help with this squealing noise, thought it was belt or pulley related but removed the aux belt and the noise is still there??
Constant noise doesn't change with engine speed....????
Tried to post a video but I'm a bit of a luddite.
It's a whistling noise sounds like it's coming from the offside rear of the engine...
Also when you remove the oil filler cap the revs don't drop, could it be a blocked EGR valve???

What year is it? Presumably it's a diesel.

Removing the oil fill cap shouldn't effect the engine at all, and isn't proof of an EGR issue. Removing the cap can give you an idea as to how much wear is in the rings. If it's ejecting lots of smoke, the rings are worn. Little or no smoke is good.

Is the noise there when stationary, or only when moving? 2009 Rimini Red SE TD4. Soon to be sold.
Hyundai Ioniq 5 Ultimate on order.
Gone. 2006 Tonga Green i6 HSE.

It's a 2014 SD4 Hse, noise is there when it's stationery, checked the hoses, pulleys, changed the throttle body, 🤔

Offside rear of engine is turbo, exhaust, EGR area.
Odd that engine speed makes no difference. Could it be interior heater fan?

Sounds you need to get underneath and have a look. Jules

I was thinking heater fan myself. But that would sound louder inside the vehicle.
Maybe the EGR valve has a strange fault? 2009 Rimini Red SE TD4. Soon to be sold.
Hyundai Ioniq 5 Ultimate on order.
Gone. 2006 Tonga Green i6 HSE.

Different engine in US but could it be?

Have you got a video of the TD4/SD4's PCV ? Jules