Toyota Repair: Knocking noise coming from engine, connecting rod bearing, oil pan

Question
I have a 94 tercel 4 sp manual with 128000 miles on it.  About 2 days ago I noticed a knocking noise coming from my engine.  The knock can always be heard but it is hardly noticeable at idle or high rpm.  It gets much louder at about 2000-3500 rpms.  The noise is present when the vehicle is stationary and the engine is revved but strangely enought the knock seems to be worse in lower gears and not as loud in 3rd and 4th.  All of the fluid levels in my car are where they should be and they have been checked weekly since I owned the car(about 5 months now).  What could possibly be making the noise and how difficult would a home repair be for a good mechanic with a basic tool set?  Thanks so much for your healp, James.

Answer
Knocking noises are always bad news, it sounds like it could be a connecting rod bearing that is starting to go, this is a major engine repair, it requires removing the oil pan and removing the connnecting rod bearing ends to replace the bearings, but since I can't hear the noise I'm not 100% sure that's what it is, but it certainly sounds like it.