Riddonkulous

I’m an onomatopoeia, a sound effect, like brrr. I’m almost the name of a hoppity guy, a friend to a famous deer. I sound like bump, and slump, and a seven hump wump of Mr. Gump. If you’re missing your front teeth, I might be what comes out when you try to say sump. What word am I, the sound when a heavy object meets the ground?