My JBL headphones are whistling before they turn off

That beeping is usually more of a system warning than an actual battery problem. The JBL Tune 670NC makes this sound when the battery is low or when it's about to shut down - it's pretty much an alert it sends out. If it's happening every time you turn it off on purpose (without letting the battery fully drain), it could be a headphone setting or even a software bug.

Try this: first, connect the headphones to the JBL app (if there's a version compatible with your model) and check if there's any firmware update available - sometimes it's just a software thing. If there's no app or it's already updated, try doing a factory reset on the headphones. Most JBLs do this by holding the power button for about 10-15 seconds while it's shutting down.

Now, if the beeping sounds really different from normal (like really high-pitched or going off at random times), then it could actually be the battery starting to have issues. At 8 months it's still under warranty in most places, so if the reset doesn't fix it, it's worth reaching out to JBL support or going back to the store where you bought it. Don't take the headphones apart for now - just let it charge and use it normally so you don't make things worse.