Buzzing noise with engine off

Hello, a couple of days ago I went back out to my 1992 Rivage and it was making a buzzing noise - the engine had been off for about  20 minutes.  We got rid of the noise after disconnecting the battery and it didn't come back with the battery reconnected.

I drove it again the next day and there was no buzzing noise after the engine was turned off BUT the following morning the battery was completely flat.

I have searched the forum for buzzing noises - can see one topic about the fuel pump, my other thought is the electric aerial which has not worked properly for a long time but is still connected -

Any ideas would be much appreciated

next time it does it remove the fuses one by one until it stops and see what circuit that fuse protects