Buzzing noise from under the bonnet when switched off proved to come from the cooling fan relay (100) in the underbonnet fuse box.     I took it out and took off its cover and it looks OK.  I have never known a relay do this before.   The car was recently flooded to about a foot deep but is going oK apart from one fan which would not stop and has been disconnected.     Is the problem in the relay or in the fan?

Curiouser and curiouser.       I took out the relay and left it.  Next day car was dead.   Replaced relay, car starts and runs, no buzzing.       Bit like a computer turn it off and turn it on again?