Battery Measures 15.5 vdc

You are being tricked the same way many of us were. LOL.
So here's the deal. The voltage you are reading is the the voltage available in the wire. It's at 15.5 V in the wires because the alternator output is at 15.5 Volts.
As you probably know, current flows from higher voltage to lower voltage.
A automotive battery will typically 'float' up over its normal 12.5ish Volt to 13.5 ish Volts when the battery is fully charged.
The ammeter is probably showing a slight current to battery because the battery is around 14 Volts and won't go higher. Current flows but instead of charging, its just cooking the acid.

Most likely the voltage regulator is the problem. Either the regulator is
a) getting the low system voltage because there is resistance in the circuits.
b) needs adjustment.

For (a) measure the voltage on the wires leading to the voltage regulator, and if different than at the alternator output (and battery positive), then also check at the ballast resistor.
With new solid state type, if its (b) then you need a new one.

As far as the alternator noise goes, try new belts and also feel for bearing play. I've also had bearings seize on these. Find a decent rebuilder if it needs a new bearing.
When the headlights are on, the ammeter should be centered. If the needle is toward discharge, it means the alternator can't provide enough power and the battery is filling in. At idle speed its a little marginal so increase the rpms a little and see what happens.
One of the other misnomers is that many ammeters are labled 'alt' for alternator.' This also has misled many of us. The ammeter in most cars that have 'em show whether the battery is charging or discharging. That's all.