(1998 S90, 165,000 miles) A day or two ago i went to start my car it did something weird. I turned the key but it didn't do anything, the electrical kind of turned on and then nothing. So i turned the key to the off position and tried it again, the car stared right up but my radio was asking for the security code like the car had lost power or i had jumped a dead battery. I didn't think anything of it, until today. This morning i went to start my car to go to work and it wouldn't do anything. I tried it again and it seemed like i had a dead battery. It seemed odd to me because i didn't remember leaving anything on and the battery is only a year old. I tried to star the car again and it clicked for a little bit then nothing so i thought it had to be the battery. I got my neighbor to give me a jump and sure enough it started right up. On my way to work though i heard this really high pitched whistle that increased and decreased with the RPM's of the car. As soon as the car would shift the pitch of the sound would lower and raise right before it was ready to shift again. I drove about 30-40 minutes to work and was reluctant to turn the car off. I popped to hood first to see if there was anything visible or if i could hear the sound and identify where it was coming from, no such luck. I finally shut the car off and tried to start it again right away. It def. seemed like it had more juice but didn't start. I'm thinking it's the alternator that's not charging the battery? but once the alternator goes isn't it the battery that runs the car until it dies too?

I guess my questions are: Does this sound like it's the alternator? Can the alternator still power the car without a good battery? Do you think i could have left something on and didn't let the car run long enough if the battery was that zapped? Any help is appreciated.