Water over hood, now unknown tapping noise

[sos3]

Newbie here, 91 300te 4matic, 250,000.
SO went through a wash here in New Mexico (only a foot of water) and washed water over hood. Car died, started 20 min later. Drove 6 miles. Air filter wet, radiator sensor apparently shorted out, no water in oil (drained after sitting overnight). Now have a definite tapping noise you can hear standing outside of car. Used tubing to ear all over but do not get any sign of increased noise corresponding to the tapping (valve cover, injectors, exhaust manifold, block, crankcase, tranny, peripherals). Have not pulled entire airfilter assembly for access to that side. Any thoughts?

Great informative site. Have learned a lot through searches. Yes, I know, 91 300te 4matic, run, don't walk away.
Appreciated,
Tom