Bingo - tried it outside cab first
No scratchy, no crackly. What is all that about then ? I can only think that the basket was slightly twisted due to uneven torquing of retaining bolts.
But whatever it was, its gone. Cab sounds very clean, with a hint of warm, even down to big flappy E on a EUB. No farty, no boomy. Its probably a 50 Lb + cab, but i can live with that.