Right - it seems as though I hadn't got the whole story.
If I apply a 10.7Mhz signal to the grid of V2 the rustling is apparent until the volume control is turned to maximum when it is much reduced. Here is a YouTube link
https://youtube.com/shorts/T72oHZQ0Xh4
If I apply an RF signal to the "live" end of the volume control there is no crackling
https://youtube.com/shorts/04CjeWVJsr0