Tomtomato, how quiet is your new motor, do you get a low level hum/whirring noise or is it completely silent?
New motor is very quiet. To be honest, I can't hear it most of the time (given speed noise, wind etc). I have probably done around 300 miles so far with the new motor, and I haven't heard any special noise once, in any assistance mode.
Motor was replaced under warranty. As the London shop was not well staffed for a few weeks (due to recruitment pending), the 50 Cycles management team got involved, they shipped the bike from the London shop back to the HQ to get it fixed (rather than having the bike staying in the shop for too long), and then shipped the bike back to me directly by courier (a large box!) a few days later, at their own cost, which is commendable.
Unfortunately, the new wiring around the motor didn't look too waterproof (visible connectors etc.) and the computer cable was damaged/exposed in the process (still working, but outer wire protection pulled).
The bike went back to the London shop (now staffed), and all has been fixed now. Computer and handlebar control had to be entirely replaced by new ones (due to the design), which is not a small task, but it was done while I waited, so the bike was not off the road.
While it took several attempts to resolve fully the issues, everything is now fine, and the bike is great.
The old motor was initially very quiet too, apart from the clicking noise, which became more frequent progressively, under all assistance modes. Also, I could feel some vibrations through the pedals...
An easy way to know if the noise is coming from the motor or something else (pedals, gears etc) is just to switch off the motor/assistance and keep pedaling at the same pace.
BTW, I believe the motor is not serviceable, so the full unit has to be replaced in case of a fault, and Kalkhoff don't sell it as a part directly to end-users, probably to protect their intellectual property and prevent retrofitting (Bosch does the same with its motors).
Despite the fault, I think the Pro Connect 10 is a great bike, with a very transparent/progressive assistance, good build quality and components, and I don't think there are many competitors on the market, with such large battery and similar components.