See my new post on the Norwegian Black Edition thread regarding lowering springs.
In short, after installing lowering springs, my i has a rumble in the drivetrain, strongest under acceleration between 40 and 50 mph, but apparent even on jackstands with the motor idling forward. On the jackstands, the suspension is at full droop, so it can't be related to my springs, but the shallower driveline angle allowed the defect to become apparent earlier.
That's my theory, at least...
2012 i-SE "MR BEAN" 110,300 miles
2016 KIA SOUL EV, 90 kW, 27 kWh, 34k miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh