I have an 85 auto and I have a unique noise upon cold weather start-up. I dont know if this relates to your noise BUT here goes!
When it is around or below 30-40 deg my fuel system makes a tapping noise like a check valve clicking. It does not last too long and usually goes away with in a minute or two. It all depends on how cold it is as to how long it clicks. The noise comes from the fuel line and is most pronounced under the passenger seat just below the door sill. Then it just goes away as the car warms up.
The injectors (like everyone else suggested ) are a source of tapping (which is completely normal) and an exhaust leak will tap too as that cylinder fires. Try removing one spark plug wire at a time to eliminate the exaust leak.
If you rev the engine up to about 2500 RPM and snap the throtle shut the injectors will almost "stop" firing as the eng coast back down to idel and if you have an exhaust leak it will also quiet down to almost nothing during the same coast down period. Give that a try and let us know if you have any luck.
If you have a CAT noise, you can bang it with a rubber mallet and if it makes a ratteling noise GET RID OF IT with a straight pipe OR a new high flow CAT
Those stephoscopes are outstanding for pin pointing noises!