Its beaten me…….almost!!
I’ve changed the rim tapes today, re-checked every spoke, put a little powder between the tyre and tube only and its still doing it. Went down to my LBS bought another pair of new tyres fitted them and its stopped. Never in all my time has this ever happened. Perhaps I have been able to find an incompatible pairing of rim and tyre. Two sets of Panaracers = Noise from hell, but a pair of Schwalbes = bliss!! Still cant work it out though, maybe I didn’t have the tyre logos aligned with the valves :)