I still cant picture what is making that plastic sound.
?
I got this album from emusic.com some time ago, and listened to the entire track last night, but didn't hear anything "plastic"-sounding.
Maybe I should get the headphones out...

Also, re. the bass drum sound: I may be wrong about this, but ... that doesn't sound like a frame drum to me. Too much sustain, for one thing. I bet Afoba is right in thinking it's boté being played.
(The deeper the frame on a frame drum, the longer potential sustain for a note ... and those frame drums above have very shallow frames.)
all speculation on my part, though!