What is causing a whining sound in my 1997 240sx?

Hello, it sounds like you have a concern with your charging system. Your alternator could be malfunctioning, which could be causing the whining noise and the battery light. However, your accessory drive belt could be dragging due to another pulley concern, creating that whine noise and causing charging system performance reduction. Hands on testing is needed to find out what is happening. And soon.

you might want to check the wiring harness from your alternator... we have had several customers with bad connectors on that wiring harness. If wiring harness checks out than have a local shop check your alternator and battery