Why is it sometimes, not always I find water in my washing machine when it rains? I am not washing at the time.

Your machine would be plumbed into the outside pipes, so there could be water coming in from maybe a crack or a broken pipe or join, this would allow water to seep in from the outside which would then eventually end up in your machine.

I would try and have a look yourself just in case the inlet is obvious to the eye, if not call in a plumber or maybe you have some insurance which may cover the instalation of your machine.

Why is it sometimes, not always I find water in my washing machine when it rains? I am not washing at the time.

How much water are we speaking of? Cheers, tom

How much water are we speaking of? Is there a sump pump in your basement?
Let me know, Tom