In most AR type buffers (I've never held a BCL102 buffer), there are three little weights. Sometimes the weights are steel, other times they are tungsten. Buffers come in different weights. On a 5.56 carbine, for example, you had Normal, Heavy and Heavy 2. Normal is 3 steel weights, Heavy is two steel weights and a tungsten weight and H2 is 2 tungsten weights and a steel weight. There is also an H3 buffer, but it's not real common.
The heavier the buffer, the slower the action cycle time, but if you run an H3 in a normal M4 carbine, many ppl report short-stroking. In some over-gassed or short-barelled guns you need the extra mass.
The BCL102 uses an AR pattern buffer, so likely it has 3 weights in it of some mix/match variety. That's probably what you are hearing.
If you are adventurous, there back of the buffer should have a nylon plug pinned on it. If you drift out the pin and remove the plug, the weights will slide out. If the noise bothers you, you could pack a couple .22 calibre cleaning patches into the buffer assembly to take up any loose space and prevent the weights from moving.