Rear end car makes loud, high pitch noise only when driving forward, not reversing and suddenly it's fixed?

Hi, let me (as detailed as possible) explain the situation:

My car has been perfectly fine for the time I got it, 10 months. Now I am leaving the USA in a few weeks so I want to sell the car. Yesterday morning, I drove about 10 miles with the car, no problems at all. 10 hours later, I start the car and when slowly lifting the brake to drive forward, the car makes a really high pitched sound. It came from the rear end, from the brakes (I think). It sounded like it could use a whole bucket of oil. It also was so loud and sounded so bad, that it made no sense to drive with it. However, reversing the car made no noise. I checked all fluids (brake and transmission fluids), both good. Then, I was done with it and wanted to park it in a better spot, drove a bit more forward in one go, and the sound was gone all of a sudden. I paddled the gas max throttle, braked heavily, and both worked just fine. Maybe you could still hear that high pitch sound (which did not sound like a scraping sound if you ask me), on volume 1 still compared to volume 100 earlier. So barely notice able.
The weird thing is also, how come that I drove it perfectly fine earlier that day, and when starting the car after 10 hours it sounds terrible? The only thing what changed is that it got way more humid out.

My question: What could this have been, did it fix itself, and should I bring it to a garage? Keeping in mind that I want to sell it in two weeks, and really want to avoid costs at this point.

Thanks so much for reading and helping already!

Hyundai Sonata GLS 2006

Your car has rear disc brakes.There is a metal warning tab on one pad that is designed to squeal when your brake pads need replacing. sometimes they beak off and stop making noise.

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At first that is what I also thought. But then, wouldn’t it be weird that just comes out of nothing? Since I drove the car to the parking spot after a 10 mile drive, no problems at all, and then 10 hours later I start the car and it is from the get-go

Also thanks for thinking with me

I have had a rock that has gotten stuck somewhere between the rotor and caliper while driving on a gravel road. it made that sound until I reversed and it popped out. just a possibility.

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Could have been a little rust on the disk too that made contact with wear indicator. Even if it was the wear squealer, there still would be sufficient pad left. Anyone buying a used car should plan on wear items like brakes etc. if the noise is constant, then you might need to take care of it. Someone would just need to pull the wheel off to take a good look at the pads.

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Thanks for helping. Since I can still break perfectly fine, and the noise seems to be gone, would you reckon I can just keep on driving it? Personally I only need it for like an extra 100 miles and then I’ll sell it.

Yes, go in peace. It should only squeal though when you brake.

The wear indicator on the brake pads squeals when you are nearing the end of the pad’s useful life. You probably have enough life left to go another 100 miles, especially if they are not stop-and-go miles. I would let it go unless the squeal comes back.

If you sell to a dealer, don’t worry about it and don’t tell a private party that it needs new brake pads because you heard a squeal. If someone asks about unusual noises, disclose the squeal and tell them that it went away. Again, just because the rear brakes are noisy doesn’t mean that they need to be replaced as shown by a couple of other responses above.

Helpful answer, thanks. I’ll let it be for now and just drive off, and pray the noise doesn’t come back. I will be supportive and if the private party which might buy my car needs new brakes first two weeks, we can split costs or something

That would be nice of you but always sell as is where is, no guarantee. Depending on the buyer they could chisel away saying you opened yourself up to providing a warranty. Not every buyer is nice Or honest. Dog eat dog.

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I’d sell as is too. A prospective buyer can take the car to a shop for a prepurchase inspection. If something isn’t found in the inspection, I wouldn’t honor a repair. If you do let them have it inspected, make sure you get all the info off a valid drivers license. Make sure the license photo and personal info matches the guy in front of you.

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Thanks for the help @bing @jtsanders , I will just sell as is. I sort of know the potential buyer, so Ill see how guilty Ill feel if it were to break down.
Ill be gone from the States so I wont have to worry much lol

Suggest to ask your shop to inspect the rear brakes. Can usually be done (on disc brakes) by simply removing rear wheels for a look-see. If pads are near wear limit, either replace them or inform buyer pads need replacement. since you’ll have to give the buyer a discount for this, probably better to just do it before selling it. Then you’ll have a selling point to boast about, new rear brakes, rather than having to explain what’s causing the noise.

And there’s upside to this approach. Some chance the problem is just a small pebble, and removing it will solve the squeal straight-away for little in the way of a shop fee. The shop can measure the remaining pad thickness while doing the inspection.

It’s not uncommon for the wear indicator to squeal for a while then stop for a while until the pads wear more, at which point it will squeal every time.