My thought would also be something left on the landing panel .
As DM says , they inspect various safety critical items underbonnet , including brake & fuel lines for corrosion or leaks , security of battery , body corrosion around strut tops and probably more .
As DM says , they inspect various safety critical items underbonnet , including brake & fuel lines for corrosion or leaks , security of battery , body corrosion around strut tops and probably more .