I still to this day don't know the explanation for this, but about 10-15 years ago I would take my mom's car, and a human whistle noise would come from inside the car. This is before the key was in the ignition and the car was completely turned off. It wasn't the car. It wasn't the radio. There would be no one else around. Usually it would just be one whistle and it wouldn't happen again while I was there. Because of that I started thinking I was going crazy. Did I really just hear someone else whistle in this car? How tired am I? Am I hallucinating? What kind of car problem could emulate a human whistle? It didn't happen every time I drove her car either. One time I was actually in the car with her and my dog. We were leaving the mall and in the parking lot. It was just us three. She was putting something up in her purse when suddenly the whistle occurs. I know my mom isn't the prankster type but I just blurted out "Okay. Has this been you doing this?" She looks at me and said " That was you. Stop playing around." I saw the look on her face as she quickly shook her head and it was basically a look of denial. If you've ever seen something or experienced something weird you know the look I'm talking about.  I say, "No that wasn't me..." For the first time it whistled more than once in one encounter! We both look back at the dog who just gives us a blank stare. It was weird though. It was as if he was just as curious and concerned as us as he started back at us. Usually he looks out the window. The whistle goes for a third time. My dog does the funny head tilt that dogs do when they try to interpret an unusual sound to them. My mom yells "This isn't funny! Stop doing that!" Which I replied with " It's not me! I'm right here you can see me!" The whistle goes off again. The crazy part was how impossible it was to try to triangulate the whistles. It sounded as if it was coming from the ceiling of the car (an older Honda Civic) one time and then under the car seat another time. We never figured out where the hell the whistles came from. All I know is it was clearly a human whistle, it came from in the car, and it couldn't have been some electronic device. Not only did we check, but these whistling moments happened over the course of about 2 years. Completely random and always weird. It was never scary though. Just extremely weird to make you think you're losing your mind. 

_{If you have an explanation I'm all ears! Either that or we had a haunted honda civic which is weird af lol}