Richard,
My VX had a similar problem, With a bit of hard driving it would always rattle from the followers, I changed all the followers to no av avail. I changed the sump foam although CC had done this 2 years ago, what I did find was the oil pick up pipe was touching the bottom of the sump pan, after bending it up and adding some Valvoline racing oil the problem has never returned even when on slicks. Maybe yours has a similar problem?
Cheers
Neil