My 2002 Ford Focus SE has started making noise whenever I turn left or right and brake at the same time. It sounds like it might be coming from the rear of the car but I am not really sure. It has new brakes all around, new rotors on front, new brake cylinders on back, and new wheel bearings on the left front and rear. Is there a simple test that I can perform to narrow down whether the CV joint is going bad or if it's the remaining wheel bearings?

If the noise is worse, when you turn to the left, the right wheel bearings are likely bad. It's not unusual for rear wheel bearings to wear out first, since they are not as "beafy" as front wheel bearings. If the CV joints are going, try driving in small circles in reverse--the noise should be worse.

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Typically, front wheel bearing/hubs and rear wheel bearings will need to be replaced around 100,000 miles. Ditto for front and rear struts. A squeak sound, when you turn, can be from the worn bearing on the top of the strut. If the boots on the half-axles are in good shape, and you're not hearing a clicking sound when you back up in small circles, they are likely okay. Ford half-axles are well made and very tough. Go with Timken wheel bearings, when you replace these components. There are a lot of inferior bearings on the market these days. Timken is usually the OEM for Ford.

Here's how to replace rear wheel bearings, which are easy to do:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-9.html#post1653648

Even though the instructions are for a Ford Taurus, the basic procedure is the same for your Focus. This might save you a little money. If the bearings are bad, you will likely see pronounced bluing around the hub--caused by intense heat.