90W AC Adapter - Buzzing/static noise when 9-cell Battery fully charged. Studio 15 Direct Base

Hi All,

I have a studio 15 (S511214AU) running on a 9-cell battery. I am charging the battery with a 90W AC adapter.

When the battery is fully charged (100%), the 90W AC adapter starts to make a soft buzzing/ static sound. This only happens when the battery is 100% charged. If the battery is in charging mode, no buzzing/ static sound is emitted.

I'm not sure if this is normal. Anyone with a studio 15 experience this situation?

Thanks.