If it happens when going round a corner, it could be an oil surge? The oil in the sump 'gushes' to one side as you corner and gets sucked up through the breather? I dunno, it might be. A properly welded in baffle plate cures this.
Or is it all the time? Check the manifold and the pipes around the cat.
It's easy to blame something for driving too fast though, it could be a total coincidence and something's just worn out through wear and tear.
"C20 LET bang"