1998 Chevy Suburban Low Battery Charge/Squeeling Noise

Ok, at points when the car is running the battery charge gauge drops from 14 (near the middle) to somewhere below that, it varies greatly. This is also accompanied by a high pitched squeeling noise from somewhere under the hood, and the lights dim.

This has been caused so far by;
-running the lights, radio, and heat
-running the rear-defrost
-turning the wheel while parked or at very low speeds, usually in a parking situation
-lifting the snow plow

some times the engine doesn't turn over very quickly when starting.

We just replaced the starter, power steering levels are good, all the fuses are good, it happens even when the snow plow frame is attached to the vehicle and battery (we disconnect the entire thing during the summer).
The alternator has been replaced ( not new but one that we are about 99% sure works)