The insect that makes all the noise in the garden is what the Spanish call chicharra - we would call it a cicada.
Sadly not my photograph
Cicadas like heat and do their most spirited singing during the hotter hours of a summer day. In fact it seems the hotter it gets, the louder they become.
Only males produce the cicadas' distinctive sound which can be as loud as 120 dB at close range - among the loudest of all insect-produced sounds.
It can be difficult to determine which direction the cicada song is coming from, because the low pitch carries well. They also seem to sense your approach and stop "singing" when you get close making it difficult to locate them.
One thing for sure, you can't have a nap outside when one is in full song.