Toyota Repair: Is it my oil pump?, sound fades, decent plan

Question
QUESTION: I recently bought a 1995 Tercel.  Everything was fine when test driving it.  But when I started it cold the next morning, I noticed a consistent, ratchety sound coming from somewhere around the timing belt housing.  It was almost like how maybe an alternator bearing "whines" but with that distinct ratchet sound--kind of like if there was something rubbing against the underside of the timing belt or camshaft gear.  But within about a minute, the sound fades until it is inaudible.  I used a rod for a stethoscope, and it is most audible when I touch it to the oil filter.  This reluctantly leads me to the oil pump.  But I find that hard to believe because it is so rare that they go bad.  My thought is that the engine could be full of sludge and that it is restricting the oil screen, causing the pump to run a little dry upon startup when it's dead cold.  What do you think?  How do you suggest I proceed?

Maybe I should add that the oil idiot light does work and it never has come on--so I'm assuming the pressure is marginal at the very least.

Thanks,
Jim.

ANSWER: I would recommend having the oil pressure tested,it may be way too low, the pressure warning light was probably disconnected before the car was sold to you to mask this problem.

---------- FOLLOW-UP ----------

QUESTION: Hello again, Ted.  Please disregard the previous follow-up question (sorry--oil pressure is completely new territory for me).  I double-checked the oil pressure.  Apparently, I didn't allow the engine to warm up sufficiently.  This time I waited until the cooling fan kicked on.  The needle on my gauge went down.......and down........and down to 29 psi at the lowest.  The engine is still quiet as a mouse and runs really well.  So I feel like the next step is to clean whatever parts of the engine I can get at, and replace the oil pump (I have to do the timing belt anyways).  Does this sound like a decent plan?  Any advice on how I should go about this?  Is some kind of an engine flush product a good idea right beforehand?

Thanks again,
Jim.

Answer
The 29psi reading at operating temperature at idle is good, it should go to about 60psi at higher revolutions or did you get only 29psi at higher revs which would be no good. When doing the timing belt check all rotating components including the water pump, check the timing belt tensioner pulleys as well.