Here is my noise measurement results before and after door rubber seal and door panel sound insulation. The rubber seals have minor effect on noise but helps to keep door gaps clean. Doors are not typically a major source of noise, and M3 has already two seals keeping noise out. Therefore we cannot expect major improvement by adding more rubber seals or adding noise barrier material inside the panel(s).
I'm using a microphone and computer to record noise spectrum and repeat each measurement 4 to 6 times and each 30 s average. Then taking total spectrum average --> measurement error is less than 0.3 dB above 500 Hz, about 0.5 dB above 4 kHz, and about 0.75 dB below 500 Hz. The problem with low frequency is that there are too few data points and random vibrations may vary measurement results. High frequency depends more on wind blow, here door seals have no effect.
I've now done much more sound insulation and got about 2...3.5 dB improvement between 250 Hz and 3 kHz, door seals was the first task but gave the least benefit.