Wanted to update since my last one. After 3 days of no trips, it tripped again which concluded it was not the fridge. I continued to isolate individual devices in my room that had that occasional MCB trip during the frequent RCD trips, until one of my PC 750W power supply encountered an issue that my PC was able to power up & unable to boot up. After removing this PC out, no more trips observed for more than a week. Indeed it was one of my devices in the room causing this intermittent RCD trips.
Googling about earth leakage current causing trips, understood that it is the accumulative of leakage current of each devices that will cause the RCD to trip if it exceeds the limit. During my meddling with the fridge defrost heater, it probably caused more leakage current in my home circuit which then incur more trips & made me to suspect to be the fridge.
The lesson learnt here is that when isolating each device, need to unplug the cable from the power socket, the rogue PC that had been shutdown during times of trips made me not to suspect it to be the cause.
I was wrong about this.
A quicker method to check for high earth leakage current from each device is to use a leakage current meter & probe it with the live n
neutral wires of the device, & if the cable has an earth together with the live and neutral cables, need to exclude that from the measurement.
Saved some money of not calling an electrician to check. The PC power supply was RMA to the vendor as it is still under warranty.