Funny sound

My mom told me to pull my car out of the garage this morning to get out the mower. when i was pulling it out of the garage i heard a funny noise from the rear end. I then backed up a little and it barely made the noise. i then put it into drive for a few feet before stopping and heard the noise again. I ddi this a few times and got the same results. It seems as if the noise would be coming from the rear brakes. I examined the ground from where the car is parked. The only fluid on the ground is water from the rain i drove in last night. Can anyone help me out here?
 
it was more of a "loud bassy clicking sound". i drove it for a while and it went away. It hasnt done it any other time it rained before, dont know y it would now. Also, it didnt make the sound last night. And this question is pointless why?
 
I have a similar noise ocasionally when backing out of the driveway. It seem's to also cause the brakes to momentarily lock up as well... This happens when I lightly tap the brake the first few times. Once I pull out onto the street it always goes away.

If I had to guess, I'd go with what Whytry91 advised?