Engine noise

I have an '87 4runner and there is a noise coming from the engine. I have been told it is either the water pump or the timing chain. I have removed the drivebelts and the noise is still there, pretty much eliminating the water pump as the problem. The noise only happens under moderate throttle between 1200-200rpms. Heavy throttle or higher revs and the noise goes away. Is there any way of finding out if it is the timing chain without having to take half the engine apart.
Yours hopefully,
Sean