Everybody pays attention to loud rain.
If you’re filming something that’s supposed to take place when it’s raining, get everything wet. Roads, sets, actors, everything. People might or might not notice rain on the video, but they will notice things not being wet.
If it’s cloth, sometimes you can get away with murder, but if it’s vinyl or a rainslicker, or a windshield, you’d better plan on sprinkling it, because people will notice.