Using a Sennheiser MKH50 (high-pass filter on) to a Millennia HV-35P preamp (gain 85%), I sometimes get unwanted sounds in the form of vibrations / rumbles. Example below in a 4 second clip that has the vibration at 2 seconds.
The mic is 1.7 meters from the source of sound: Rain on a window.
It is mounted in a Rycote InVision 7HG MKIII Microphone Shock Mount on a mic stand.
Can anyone identify what this sound is and the mistake I'm making that is causing it?
Help is much appreciated.