I have 4 years old VW Jetta and when I am on highway going exactly 118km/h (73mph) I hear low pitched humming noise. It is specific to this exact speed (hence why I suspect it's resonant in origin), it get quieter when my speed varies by 1-2 km/h and completely disappears when the difference is bigger (can't hear it at all at 120km/h). It is loud enough to be clearly noticeable and cause annoyance.
I haven't been able to determine where is it coming from because I always drive alone. I hear it coming from right side, but since I am sitting on the left side of the car it might just as easily be coming from the middle. I wasn't able to determine front/rear position of the source either.
Regular maintenance service is coming up soon and I would like to bring this up. People in this country are usually not very competent when it comes to, well, pretty much anything, so I would like to know before-hand what might be the cause so I can point them in right direction.
UPDATE: I did some tests and the noise is tied to the speed of the car only. I tried to change gears, driving in neutral, tried both D and S modes and the noise still appears only at 118km/h and every time I hit that speed, no matter if I am accelerating, decelerating or moving at constant speed. Turning the AC and other electronics on and off did not have any impact on the noise
UPDATE2: I updated tire pressure to recommended setting and the noise is still there, unchanged