ker·plunk 
(kər-plŭnk)
(kər-plŭnk)intr.v. ker·plunked, ker·plunk·ing, ker·plunks
To fall with a sound like that of a heavy object falling into water.
n.
A kerplunking sound or movement.
[ker-, intensive pref. (probably from Scots) + PLUNK.]
ker·plunk adv.