Pads worn out. Dust between pad and rotor. Leading edge of pad has 'feathered' and needs filing off. Pads fitted without anti-squeal shims.
You Dont Grease It Up enough
The Squeal means its time to replace the Brake pads.
probably not your engine, sounds like its time for new brake pads. if this doesnt correct it have the master brake cylinder checked
That depends on how, when and where it is squealing. For example, if the brakes squeal when applied, the brake pads are probably worn down. A squeal from the engine compartment whenever the engine is running could be a loose serpentine belt (especially if the squeal changes a little when you rev the engine).
You can try but the squeal will probably come back. Brake squeal is usually due to cracked, glazed, contaminated or inferior brake linings.
Check the brake pads for wear. There is a metal tab attached to the pad so as the friction material wears out the tab contacts the brake rotor and it makes a squealing sound but as braking is applied the pressure on the brake pad causes the noise to stop.
Accumulation of brake dust, or brake pads that are nearing the end of their service life.
Generally new pads will contain a layer of dust which causes the initial squealing. The squeal should go away after a bit if driving.
That could be the brake pad "squealers". They are designed to squeal when they are worn out. Time for a brake job.
Squealing from the engine (ie; it alters according to revs applied) would suggest a belt is slipping somewhere. Squealing that varies according to road speed suggests that the is metal contacting on metal. If it is when you brake, I know that some Korean cars have brake pads that squeal when they are worn to the point of replacement. I had that happen to me on a Kia once, and it scared me witless to start with!
Probably the brake pads. These squeal loudly to warn the driver of impending pad erosion and urgent replacement of the same. If you continue without replacing them the squeal will get louder and eventually the brake disc (or rotor) will get damaged.
The most problematic cause is that if your brake pads/shoes are worn down to the changing point. Other causes can be that your rotors/drums are glazed (due to overheating) and or simply brake dust and other road debris.