Hi npt,
Welcome to the HP Forums!
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I understand that when you play videos from YouTube or play music with ITunes, you hear a buzzing from the audio.
Have you done all your Windows updates? Have you run the The HP Support Assistant to look for any updates and help resolve issues. Windows 8 has a built in troubleshooter, did you try that?
Press the Windows key + C to open charms
Type troubleshoot audio in the search bar and press enter
Follow the on screen prompts
Is your Direct X updated?
Here is a link to HP 15-d051sa Notebook PC Drivers, to ensure you have the current supported drivers. I know you have sound, but her is a link to No Sound from Speakers (Windows 8), that may have some suggests that helps.
If you would like further assistance, I suggest you contact HP support.
Please call HP technical support at 800-474-6836. If you live outside the US/Canada Region, please click the link below to get the support number for your region. HP Technical Support Sitemap