Without more details its pretty hard to guess, but if it was control tones, then the RCD would trip out more often than just once a day, as the control tones are sent many times a day to control various loads on the network. They are not sent only once a day. If the RCD was sensistive to control tones, then it should trip each time a control tone is sent, not just on the one at 6:30am. I would suspect if only once a day, then it would more likely be related to the load being switched by the control tones.
A common problem is that some old fridges had 24 hour timers in them to autodefrost. This would activate a heater, which often had sufficent leakage to trip a RCD when cold and damp, then once on would dry out. This would happen every 24 hours.
Changing to a different brand RCD may stop the tripping, as the replacement one may have a slower tripping characteristic or slightly higher tripping current etc. Also some RCD's can handle switching surges and capacitance to ground better than others, and often include a
10ms delay before tripping (not to be confused with the S-Type, which is delayed to allow series installation with other RCDs, and is not intended for personal protection).David