Well, there it is! My bike converted to BBS01B ebike, which suffered an unfortunate overheating of the engine which caused strange noises which therefore forced me to put it down and open it .... it's been several weeks since the electric bike was in work and finally, today, the electric bike is repaired and after a road test, everything works normally without noise! What was needed was to relubricate the white plastic gear carefully with Teflon! Everything else still seemed to be in good condition so I'm happy with bafang, although I don't understand why this overheating caused me all this hassle.