My Tucson started making a squeaking noise. It only squeaks two to three times when it does it.
When I slowly accelerate, when I slow down, and when I turn the car off. When I turn it off there’s a loud clicking sound before the squeaks.
The dealership said they can’t hear anything after holding it overnight. I shouldn’t pay $30k for a vehicle that squeaks when I drive it. This can’t be normal, can it?! Please help!
I have a video but the forum won’t let me add it 
Upload it to Youtube and put the link on here. How many miles?
I don’t know if you’re in an area like I am where the air conditioner is used most of the time. I don’t know if you drive in an area where the HVAC (heating, ventilation, air conditioning) system is likely set to a setting that would involve the front windshield defroster/defogger to operate. It can be a combination of heat/defrost/defog (Some people don’t realize that the air conditioner is running at times, even when they have the “heat” turned on). You don’t say.
Anyhow, any of the situations mentioned above will run the air-conditioning system which uses a compressor and clutch that is driven by the engine using a belt. The clutch could be creating a clicking sound and the belt can make a squeaking sound if something involving this system isn’t quite right.
So, to make a long story longer, be cognizant of whether or not the air conditioner is operating when the clicking/squeaking occurs. Try it. Turn the HVAC system completely off when it’s safe to do so and see if the noises go away. This would help determine if the HVAC system is the culprit or not.
CSA
I don’t want to make any accusations, but I have worked at car dealerships. Let’s just say that when a mechanic was given your car to diagnose, she/he possibly could not replicate the complaint.
However, I have seen situations that occurred because of how warranty repair work pays/compensates mechanics for diagnosing and fixing warranty problems. Some manufacturers pay a limited amount of money for this warranty work (compared with work they do that is paid by customers) and sometimes mechanics aren’t highly motivated to do the work, let’s say. Sometimes they conveniently don’t hear or notice anything that would lead to them being “tied up” doing some warranty work.
Here’s what I’d do… Get hold of the Service Director/Manager at the dealership and discuss your written copy of the repair order you kept, showing your complaint and the mechanic’s diagnosis of “No problem found.” Arrange to take that director/manager for a ride, long enough to demonstrate what you’re experiencing and be sure they hear it and agree there’s a problem. Oh yah, be sure all your service complaints are written up and keep all receipts.
If this doesn’t help then try a different Hyundai dealership.
CSA
Does it squeak more in the morning when you first start out, then as the car warms up it squeaks less?
It’s not normal for a 2018 model, but it’s not a rare problem either. You could type in squeak or squeal into the forum search feature, upper right on this page, and see what other’s have had to say about it. For squeals on a 2018, I’d guess some sort of drive belt problem. Try this experiment: Put a rubber band into the freezer for a couple of hours. Then remove it , put it on the counter, and watch what happens. It will sort of do a little dance as the rubber shrinks. Rubber is unusual in that it shrinks with higher temperatures. That’s why I asked about the temperature relationship above.
The dealership would fix it no problem I expect if they could experience it. But if they can’t hear it, you’ll have to wait and bring it back to them when it becomes so obvious they’ll have to hear it. They probably won’t replace parts on a guess under the warranty terms. Only if they can note a symptom.
It doesn’t ever not do it. No matter if I just start it and turn it off. Or if I’ve been driving it for miles. When I stop through a drive through for example, as I slow down, it squeaks twice. As I slowly take off, it’ll squeak twice. Then when I turn the car of it clicks a few times then squeak squeak. They told my husband if I am hearing anything then it’s normal and a part of “newer technology”. I’ll try taking it back and having someone else looking at it.
The other forum I read on here mentioned knocking but mine definitely isn’t knocking. I’ll try searching the squeal/squeak terms. Thank you 
Get a mechanic to remove and inspect the serpentine belt, then check each pulley for free play and smooth spinning.