2010 Honda Civic Popping Noises

I finally found your website and would like to ask a question. Last night, as I sat in my car not moving, it began to rain. After a while, a popping sound began coming from my back passenger door. This was the first time this had happened, so I just waited on it to stop. It went on for quite some time. I wanted to get out to locate exactly where the sound was coming from, but it was still raining. The sound would range from fast pops to slow, then it would stop for awhile, then start back up again. Do you have any idea what this could be? Thank you!