Alternator whistle sound

There might be voltage drop in the blue wire that goes to regulator, also insure good ground at regulator case. 14.9V is a volt high, there must be drop between blue wire and battery. Long term in hot weather, it will boil the battery. The drop is often in bulkhead connectors. The drop can be measured from blue wire to battery terminal. As a test, jumper + battery terminal to blue wire, see is sound goes away. If it does, fix connection problems.