2001 Ford Taurus Knocking at startup

Start by checking oil pressure with mechanical gauge.
On a cold engine you would want at least 40-60psi.

If OK, then change oil and run magnet through used oil looking for any metal particles.

If OK, then you could have a accessory drive problem, like a tensioner or pulley.

On cold engine, remove serpentine belt, start engine and run for 30 seconds, you will get alt. Light come on, but you are looking to see if knocking goes away.
If it does, then you have isolated problem to assy. Side.

If you still have the knock after above and there are no metal particles in oil, remove flexplate (flywheel) inspection plate and check that all bolts to flexplate are tight and none are missing.

Metal would indicated a bearing wear problem and would require extensive repair.

Hopefully is is an oil pressure problem that has not affected the bearings yet.

Should not take more than an hours labor. They remove the electrical oil pressure sender and replace with a fitting connected to hose with gauge.

Crank and start engine and look at actual oil pressure in engine.

If low, could be an oil pump, oil pump pick up, clogged oil galley.