Bad Alternator???

Just started noticing a humming/whining noise coming from the engine compartment of my 98 GMC Sierra with the 5.0L. This happens while at idle and when driving. I have turned off all heater controls and the radio and this still happens. Does anyone know if this could be a bad alternator or an alternator getting ready to go? Some days I do have trouble starting the truck as well. I thought that it was the battery getting old but maybe the battery just isn't getting charged properly.

Any help would be appreciated.

Hi: how long has the batt/alt and starter been in service (kms on the truck). if you have a long screwdriver place you thumb on the end of the handel like you were going to jab the counter. now place the joint of your thumb to your ear and carefully place the tip to the Alternator frame with the truck running, you should hear the same noise just louder. you could use a mechanics Stethoscope to do this if you have one or access to one (looks like a doctors with a 6 inch /15 cm rod on the end of it). this is used to pinpoint sorces of noise in a high noise area. you could remove the belt from the truck and start it and see if the noise is gone. have a load test performed on the stater and a load test on the batt to tell you the state of there condition. if your not sure ask before you start. 463

Thanks for the tip. I did a little searching and found out that my positive battery terminal connection was loose. This was causing resistance to build up which was causing more current draw. The alternator was working to hard to keep the battery at the right voltage. Tightened up connection and the noise went away and the truck starts a heck of a lot better. Apparently this is a pretty common problem with these trucks.

Moral of the story. Check the cables often.

Thanks for the advice.