This is a building site. We have been told this from what George says. However the whistling man is in the foreground and the men around the wheelbarrow are in the background, which suggests that George and Lynne are walking right through a building site. This is very dangerous. They are not wearing hard hats or brown coats with high visibility stripes on them, therefore the builders must know they are liable for the safety of the George and Lynne. The man in the foreground knows this is a lawsuit waiting to happen.
Normally we would assume that the foreground builder, not to be confused with a foreman, is whistling a wolf-whistle. Now, even though my knowledge of reading music is pretty poor I am sure that the tune he is whistling is not a wolf-whistle. A wolf-whistle will consist of three notes, two of which are joined together. The tune the builder is whistling has eight notes. It starts with three quick notes together, which look pretty much the same, followed by two close together which go up. Finally it has one short note followed by 2 short notes going down. So just a tune really. It's a wonder why George and Lynne have such a problem with the man's whistling. Perhaps it's just awful and Lynne is a purist of music while George is more of a fan of the blues; neither of which should contain any whistling.
The man in the last pane must be the foreman. He is not wearing a hard hat but a cap instead. This may show his seniority as he rarely actually on site but stays mainly in the site office looking at designs and making phone calls. He also wears a different shirt to other builders on the site. But why is he smiling? Perhaps he also heard the whistling and is about to join in for a communal Roger Whittaker recital. It's either that or Over My Shoulder by Mike & The Mechanics.