Grinding noise around 50km/h (30mph)

Hi there,

I drive a Twizy 80 Technic from 2013 with 11.000 km on the clock. When I drive around 50km/h constantly, you hear a high frequent grinding noise. It stops when you slow down or accelerate.

The Renault dealer (also ZE certified) already replaced the differential, because they saw that was in bad condition.

But what is this grinding noise coming from? I’ll contact my Renault dealer soon, but wanted to ask some more experienced owners first ;).

i had the complete gearbox changed for the same reason at the end of last year with only 1000 miles on the clock

When I changed my gear oil to the Mobilube, all noises stopped.
I do get a low vibration range at that speed, especially releasing the acceleration. it feels like driving over gravel. Could be asphalt roughness but I fear friction