In my apartment I always had the same problem with D2 at ~146Hz. It feels like a deep hum. The distance between speakers and wall is about 2.38 meters, so
f = v / L L = v / f ---> L = 343[m/s] / 146 [1/s] = ~2.38[m]
means something like the lenght of the wave (L) is equal to the distance between my speakers and the wall. I guess this is called intrinsic vibration modes.
Is there a way to mitigate this phenomenon?
EDIT: Here's an audio. If I playback that audio file through the speakers the hum effect doubles its intensity ! D2 note isn't even distinguished.