Do you have any of these in your home?
If you do, please start by removing them?
The following can also play a role. Old Alarm transformers are also well known to cause this.
Basically every thing with build in surge protection will contribute to your current situation.
Lastly, it might just happen that your earth leakage is on its way out and that its sensitivity is not on 30ma anymore. I do respect @plonkster previous experience with the earth leakage and that buying an very expensive RCD fixed hie situation but before I even suggest that solution we try and eliminate all of the above first. 95% of the time its one of the devices above, 4% sensitivity issues and only 1% required that expensive RCD as we could not fine any other reasons.