It’s not the rain, it’s the pings. For much of the day there is a faint metallic ping every 3.6 seconds or so. Like this, but with less reverb:
It stops and starts – can’t say how often because the volume is low enough that it quickly fades from notice.
Non-trival sized buildings in Hua Hin stand on pilings about 40 feet long. They’re driven into the soft ground by a pile driver. The machine is automated, hence the regular 3.6 second interval. Next the tops are cut off. Workers dig a deep square hole around the pile then connect the holes with shallower trenches. Tie everything together with rebar, pour concrete then bake until it’s a foundation.