it may be a warning that your alternator belt is too loose. This usually can be easily diagnosed and should be fixed as soon as possible. You can probably handle the job easily, quickly, and with tools that you have aboard.

First, check the alternator for significant problems. If, for example, the belt is rapidly deteriorating or a mechanical part is interfering with the alternator, shut down the engine if it's safe to do so.

Then check for an increase in the DC alternator load. Examples of this could be from 12-volt refrigeration, a 110-volt microwave powered by a battery-fed inverter, or even a wiring short that you'd probably find by seeing "arcing" (sparks or electrical discharge), a burning smell, or even fire.

Confirm at the 12-volt panel if possible; if there's excess electrical draw, turn off or fix the device. If the extra loading has occurred before without squealing, or if squealing continues after you turn off the DC load, then it looks like the culprit is a loose alternator belt that needs tightening or replacing.

Keep in mind:

Fine belt "dust" around or under the belt's path could indicate any of the above or misalignment of pulley wheels, but these particles are normal to a limited extent after lengthy running.

Misalignment of wheels is usually best determined by removing the belt and putting a straight edge into the center of the grooves.