Help requested

[The Truckers]

I'm new to ebikes, I have bought a Kalkhoff Agutto 2016 with 1,740 miles on it. Generally very happy with quality bike purchase, power and range. However I'm getting a cracking sound and a little slippage, I think,from the hub when I change from 7 to 6, absolutely rock solid transmission in top 7th. gear so not thinking it's chain or rear cog wear.
I am entertaining your experience & comments ladies & gentlemen regarding my 'hickup' .