Brake Squeals

Most commonly, that sound would be coming from your brakes. Have you had them checked or replaced recently?

Brakes will squeal if they get worn down too far and require brake pad replacement. Sometimes they will squeal in perfectly harmless condition such as when they get wet, which should clear up quickly as they dry, or if they experience too much vibration. New brake will also sometimes come with either gaskets, metal clips, or a sort of anti-vibration grease or putty to reduce squealing from harmless vibration.
In any case, I would recomend having somebody knowledgable (or service center) check the brake pads for wear and replace if neccessary.

On more rare occassions, the squealing could be coming from other sources such as being in need of chassis lubrication, axle grease, and so forth. Most more serious mechanical wear or failure would sound more like a grinding noise.

Is it a tire squeal or brake squeal?If it is brake squeal put high temp synthetic brake lube grease behind the brake pads to reduce/remove the brake squeal.This allows the pads to sit on a bed of grease and will not vibrate at the frequency which produces the squeal.

To address your first problem squeaking brakes aka "brake squeal", is most often casued by one or 2 things: "Pad vibration" or a "low brake warning sensor".

Pad vibation is usually caused by ineffective pad anti-rattling clips & hardware that allow the pads to vibrate at a super fast speed whenever the brakes are applied, thus causing a high pitch brake squeal. To correct this, replace all the pad hardware and anti-rattling clips and make sure you use a quality pad set that has anti-rattling plates attached to the backs of them. Weather conditions do affect brake squeal, that is why it seems to be worse at times.

Low brake warning sensor squeal occurs when your brake pads reach the point of replacement, the sensor attached to the pads scrapes on the rotor which produces a high pitch squealing sound to warn you it's time for new pads.

As far as your second problem goes (a knocking sound), I'll need more information about the problem before I can offer a possible cause (eg. happens on left or right turns, while going over bumps, at high or low speeds, accellerating...).

There are 3 to 4 different compositions of brake pads--some are softer--others are ceramic or metallic---probably you have gotten metallic---which do have a history of squealing much of the time. therefore, check to see if that is what you purchased--if so--there is no mechanical problem. However--a tip--especially in colder, salt-using, (on streets)climates. Lubricate the brake rotor sliders with grease twice a year so they don't stick.

The noise is probably due to the brake pads themselves. When I fit pads I either coat the back of the pads with anti-squeal compound or the face of the caliper pistons with copper-ease grease. The presence of either prevents high frequency vibrations that are the cause of squeal. If you use the grease method be very careful not to get any on the discs or pad facings: grease is a lubricant and the brakes rely upon friction in order to function so the two do not go well together.