Humans aren't good judges of how often they dream. You have REM sleep several times a night and generally if you're woken up during REM sleep you will say that

Humans aren't good judges of how often they dream. You have REM sleep several times a night and generally if you're woken up during REM sleep you will say that you were dreaming. It is probably more likely that you are simply remembering dreams more when you can hear rain on the roof - either by power of suggestion, or because the stimulus of the rain noise is noticeable and memorable in your dreams, or because the rain itself is waking you up. This isn't to say that you're wrong - there most certainly is an effect - but whether that effect is positive or negative is unclear.