Strange Noise

[jsnmac]

This is a bit of weird one but hopefully someone might know whats causing it. A couple of days ago my A4 130 Tdi started to make a noise like a geiger counter. The noise is coming from behind the panel in the boot just below the fuel flap. It does it non stop even when the car is locked. I am wondering if it has something to do with the central locking as the noise changes to a pulse after the car has been locked. It isn't very loud and it doesn't seem to be doing any harm (yet) but is very strange. Any help would be appreciated.

Many thanks,

Jsnmac

[GeorgeE]

Just guessing, but the two items in that area are the alarm sounder and teh bass speaker/amp. Could be either one of those I suppose.

[RickT]

The back up battery on the alarm siren is flat..

Rick

[jsnmac]

Thanks for the replies, i will get them looked into.