How do you know that isn't the noise Horn Leech makes when it hits something that's normally effective? Listen to the noise that Flame Charge makes when it hits Helioptile. That sounds like a Fire move hitting something, not a normally-effective move.
AND this is assuming they keep the same noises, don't change anything, etc.
NO MORE HOME ROWED BECAUSE I'M A GOOD GIRL so drag me down to the ocean floor, 'cause i don't wanna fight no more