Any noticeable differences in frequency profiles? I've not used Decibel X but my understanding is that it can do some basic spectrum analysis.
I've used some android equivalent on a Samsung S8 in my model S75D and found that the body has a distinct resonance at around 70Hz which is amongst the lowest I've measured on various cars. They were resurfacing the freeway on my way to work and had dimpled the surface to improve adhesion. Well let me tell you, at around 80kph the car droned so badly that it could shake out fillings. The 70Hz definitely needs more damping.
On a normal surface however where the resonance doesn't get pinged levels were around 52-56dB.
What we really need is an app that does A-weighting measurement to see what the human ear is actually going to hear.