Noise at Idle - Solved

My 2012 1.4 TSi had a distinct buzzing noise when idling, clearly audible both inside the cabin and from under the car.  The slightest increase in revs stopped it.  I had visions of failing timing chain or AC compressor, both £££ jobs.  After much investigation the cause was found - a loose fuel line.  There are two fuel lines, black and white, which run from the filter next to the tank forward to the engine bay on the driver's side (RHD).  After removing the plastic underbody cover (8 captive nuts, 10 mm AF) and the resident spiders, it was clear that the pipes are well cleated at the back half.  However, the front half of their run is within a box section, and probing with a finger through an oval slot on its underside it was clear that they are not cleated inside but free to move about.  This was the cause of them buzzing against the floor, at a point just in front of the driver's seat. I am not sure whether this is vibration being conducted from the engine or the pulses of fuel in the pipes making them move.

The cure was to add some plastic foam against the pipes, with a stout plastic tywrap on top to hold it all firmly into a corner of the box section.  Fortunately there was already a small hole in the side of the box section level with the oval slot, so the tywrap could loop into the slot and out through the hole.  Total cost to me - nil.