2k Prelude "clunk, clunk, clunk...."

My 'Lude develop a mild "clunk, clunk, clunk..." noise
from the timing belt side of the engine.  When the RPM 
peaks to max and at the moment it drops (like if you 
quickly press and release the accelerator) that's when 
the noise can be heard.  It can also be heard (and most 
noticable) when the RPM is steady from around 1K to 2K).
    Is this the water pump?

TIA
Andy