Loud whistle noise

If it is a belt.... there is only one serpentine belt.
Does it go away after it warms up?
In the 90's Ford had a problem with the EGR valves that would "hoot" until it warmed up.

make sure that the pulleys of all the driven equipment are in alignment and not at a bit of an angle to the axis of the drive belt
To break belts something is not lined up properly or something is not turning freely

you may have a vacuum leak

well it may help if you open the hood, then start the car and see if that helps you locate the item which is whistling. many cars have a power steering pump which likes to whistle until it gets warm. generally this is less than 5 minutes, and that is more like a screeching sound. something is either blowing out or sucking in through a small orifice to make the whistle, you need to physically locate the source of the sound. many bearings are in there spinning and any of them can be doing a cold screech.

myself I have been know to use a BFS, which is a big long screwdriver, i touch the pointy end to each of the spinning components and put the handle end to an ear. yes this process is not suggested for people with long hair or just no damn sense. but as i move the pointy end from component to component i know immediately when i touch it to the screechy one.

Replace the gasket between the air manifold and the CFI.

If it is whistling while you rev your engine (while parked), then most likely there is a leak or hole in your air intake or vacuum hoses.

Facts:
1. Your car creates a vacuum to constantly receive air from the outside.

2. A whistling noise is created when air travels through a hole.

Check all air pressurized ducts for holes or leaks.
Check air intake system for holes or leaks.

I had a problem with a whistling car after 50 mph and it turned out to be the front window gasket. I put silicone on the trim and problem solved.

This is normal unless it is really loud

Sounds like a vacuum leak. Check that all your vacuum lines are attached and in good condition.

volvo s80 y reg 2.4 runs ok little bit lumpy tickoover when warm but very loud whistling noise take dipstick it stops but very big suction from tube not pressure it is not breather box under manifold