2007 civic runs rough in the rain

I just drove home in a heavy rain and I noticed that the engine was getting a little loud at times. It seemed to be at low RPMs and when I punched the gas a little harder, it went away. It was hard to hear clearly through the rain but it sounded like a car without a muffler. Does anyone know what could be causing this? It’s not all the time but every once in a while, I noticed it maybe 3 or 4 times in a long trip. Thanks.

If The Exhaust System Has A Flex Pipe, I’d Check It.
CSA

Do you think that it’s more than a temporary problem? I was thinking that maybe the exhaust got splashed and cooled down a lot, changing it’s size and leading to a change in the sound.