So this has been a very weird case for a few months.
We have sent at least 6 different plumbers there for over 10 times and nobody could find out the reason.
What happens is sometimes when the washer is running on the main floor a lot of water pours out from ceiling in the basement. But this only happens SOMETIMES.
The plumbers came and tried to recreate the leak but it just didn't happen while they were there. The basement ceiling was opened up so we could clearly see the pipes. One leak was caught on video (when there was no plumber around) and we could see a fair amount of water came down from the pipes.
We showed the video to the plumbers BUT none of them could find any holes or cracks on the pipes!
Anyone experienced similar issues?