Intermittent Whistling Tea kettle noise
 

I have a 2019 Sonata Sport. Ever since I got my new car I have been experiencing an ongoing intermittent issue dealing with a whistling Tea kettle noise. It occurs while the car is either stopped or moving. This is the absolute best way that I can possibly describe it. The noise appears to be coming from more towards the front of the car. I am wondering if I have a vacuum leak somewhere?

I am still experiencing the intermittent yet frequently occurring whistling tea kettle sound coming from the engine bay area of my car. This noise occurs while driving, parked, or stopped. The dealership failed to fix it, but they did offer me a $25 oil additive to protect the engine from heat. I said NO.

If you are able to do this,
Can you open the hood of the vehicle, start the engine and see/listen if you can determine just about where the sound is loudest. Vacuum leaks can and do make whistling sounds, but not all the time. Without being there to do this , it is practically impossible to offer any worthwhile suggestion.

This sound can be best heard from the cabin or front seats. I am unable to hear it from the outside even with the hood open as the engine noise drowns it out.

IF,,,,,,,,,,it is a vacuum leak, then it very likely might be close to the firewall in the engine compartment or maybe even inside the vehicle.

A good visual check of all vacuum lines might reveal the location or an old mechanic's trick , if you can use a piece of rubber hose with one end held close to your ear and search around where you seem to get the loudest reading. Just be very careful around moving and hot parts doing this.
Sometimes this will also let you know if it is not a vacuum leak.

I am really starting to wonder if my alternator is beginning to fail. I am having issues with my heated front seats being very slow and weak to operate, even while on the high setting. The heater now only works if the temperature degree setting is really cranked up, and the tachometer needle now nervously fluctuates up and down while idling. I am also feeling a pulsating shuttering vibration as I depress the brake pedal. I just had the service campaign 953 for knock sensor detection system software update installed last week. With the exception of the intermittent yet frequent whistling tea kettle sound, I have never experienced any of the above mentioned problems before.

If I understand you correctly, these problems appeared after some work was done.
If this is the case , I would suggest you return to the place that did the work and have them recheck their work. There is a good possibility they might have overlooked something.