Sound from washing machine use - findings

Recently, when our washing machine was in use, I heard a sound that is similar to the one generated due to the rotation of some coin or similar one or from the impact of fashionable hangings on clothes, in the drum. I removed all clothes from the drum, drained the water, but could not find any.  Tried again with clothes and water in the drum and the same sound was heard. Then, I made empty runs of the drum with water alone and the sound could be heard again. But, there were no openings under the pulsator (shown below). Another attempt at the empty run with water gave sound again. Then, I tried to remove the pulsator, without success. But, I could remove the filter over the drain inside the drum, as shown with an arrow, and then operated the machine with water. After a few minutes, I saw, suddenly, a one rupee coin pushed into the drain (as in the picture). I am clueless still, how this coin found way to down below. But, my problem is solved and then I fixed back the filter again, though with some difficulty. 

As the saying goes, listen to the machine to understand the problem, I could find the problem from the sound and thus avoid damage to the machine. Posted for information.