It has taken me a while to figure out how to measure and interpret the vibrations. The vibration intensity and frequencies varies by location in the house. Also, there are limitations to what I am able to record with the data logger I have.
The best way to see when the vibrations occur is to look at time series data. Time series data shows just that, vibrations recorded over a period of time.
Here is a recent week of nightly measurements. Time series data shows just that, vibrations recorded over a period of time
This shows the vibration in acceleration versus frequency for a single direction. The image is the result of an analysis of 5 minutes of data recorded at the sampling frequency (raw), in this case 4,000 hz.