Have you checked the belts? A squealing sound can indicate a loose or worn belt, or slippage of one.
If it is a "whine" it is probably the compressor, which could run for a long time or it could give out tomorrow.
whining
something may be rusty
Whimpering is to make low, whining and broken sounds as in crying or in fear
Howled: to make a whining sound; to cry out; to express loudly.
A panda cub make a high pitch whimper A 3 month old makes a deeper sound than a newborn And sadly an adult sounds like a pathetic goat.
Two components in a PC that might make a whining sound are power supply and disk drive. Noise from a power supply usually means it is time to replace the power supply, however, it might just mean that the fan is dirty and the dust needs to be blown out with some compressed air. If your hard drive is making any unusual noises it is time to make an immediate backup of your data and replace the drive.
low fluid, internal bearing failure.
A whining sound coming from the front of the engine would make me think one of the bearings is wearing out in the belt assembly. This is something you should fix promptly.
fluid braking down
if it sounds like a high pitched whining then it may just be your cool air intake
Normally a whining noise in the back end means the differential is shot
Low on P/S fluid and/or air in the system.