Ford focus brakes squealing?

My Ford focus from 2006 has gotten both front and rear brakes replaced this year. The squealing or screeching is coming from the rear. It's only when I back up or when I break in general. Sometimes it's quiet and others very very loud. It's not because the brakes are new either. I got the rear ones replaced in January. They are drum brakes in the rear.

Here is what they sound like

I went to my mechanic and he said the brakes are fine. Could this be a lubrication problem? Or could it be my rotors?

How to upgrade my 2017 Ford Focus SE sound system?

I'm wondering if there's an amp already in the unit somewhere so I can potentially hook a subwoofer up to it.
I'm a skilled craftsmen and I'm planning on making a bandpass sub box. I'm aware that the amp that s possibly installed won't produce an impressive amount of watts but if I keep the factory speakers and make a bandpass sub box I should be able to use the remander of the watts to get a decent sub, right? I also want to plan for when the speakers go out, so is buying a new amp the best option? I also need advise on what sub to get and how to take off the front panels properly

How do you find the keyless entry code for a 2009 ford focus?

How do you find the keyless entry code for a 2009 ford focus?

Added (1). I bought the car used and the card that has the code on it wasn't with it and the dealer wouldn't recover the code with me paying a crazy high fee. My opinion I bought the car and the code should come with it free of charge.

How much would it cost to drive from San Diego to Oregon?

My friends and I are planning on going on a little trip up to Oregon. We were wondering how much it would cost and how long would it take for us to get there. We're driving a 2014 Focus Ford car. If anyone can help me on how much gas money you think we would need or anything else that would help a lot, thanks!

03 ford focus ZX5 will crank but not start

I have a 03 Ford focus ZX5. There was a loss of power to the engine while using the on ramp for a highway. Pulled over for 2 minutes and then it drove fine for 20 miles to my house. Next day started fine and in less than one mile there was loss of power again and then wouldn't move. Shut off engine and now it will not start. Replaced the battery, fuel filter and checked spark plugs.

Rattling sound at 1,600 rpm?

2011 ford focus with 100k miles, at exactly 1,500-1,600 rpms there's a strange rattling sound coming from under the car near the front. I think its possibly something in the cat thats loose but i don't know. Any help is appriciated. Btw it always happens evertime i hit that rpm