Weird Noises

When in 2wd and im on the gas there is this weird sound coming from the front almost like a bull frog sound. Its hard to describe but thats the best i can. It goes away once i go faster either because i cant hear it or it has gone away. Also when i put it in 4wd and let off the gas there is a almost like grinding sound coming from the front what could be causing these problems. Are they related? Thank You.

I have a better way of describing the sound when in 2wd. It sounds like something being stretched out like piece of rubber or something. Thats the best i have lol