On Monday, July 22, 2019 at 4:01:58 PM UTC+1, gregv wrote:
Le lundi 22 juillet 2019 16:07:24 UTC+2, Tim Taylor a écritÂ*:
Likely the canopy or spar. Clean the canopy rail and the area where it touches on the fuselage. A light coat of wax or a very thin open cell foam seal may help on the canopy. Check the spar for rubbing and wax any possibility areas.

ok thanks, I think it is spar related, I will wax and check for rubbing

I used to have a Nimbus 2c. It was a long time ago but I still remember what I think is the same cracking sound you are describing. Quite loud and sharp. It never bothered me. Like you I thought it came from the spar stub area when there was a bit of turbulence.