Ford Ranger 96, went to get in noticed a buzzing sound and battery gauge was going crazy! Everything else seems fine and once I started truck up gauge went back to normal but still have sound. Any ideas? PS. Battery is new

 

Depending on where the sound is coming from, it sounds from your description, like a relay attempting to energize and releasing at the same time..
A good part of the time this can be caused by an unintended path of current which is not high enough to completely close the relay or the relay actually leaking current and dropping out, but at a rapid pace.
Sometimes corrosion will allow a poor path for current to flow and result in a problem like this.
What you might try is to use an old standby and remove fuses one at a time and this might help isolate the area when the fuse is pulled the power in that area is removed.
There is always the possibility of a faulty electronic component malfunctioning and removing the power to that component might help pin down the area.