buzzing and lag issue

Hello,

I have the following HP Notebook :

HP Pavilion Notebook PC

Product No: F4T58EA#ABU

OS : Windows 8.1 64-bit

Intel(R) Core(TM i5-4200u CPU @ 1.60GHz

mem 8gb.

The problen is when I watch a video every couple of seconds I get this buzz sound from the speakers and headphones. I have re-installed factory drivers and it stops but returns later. There is also a small lag with the notebook. Any ideas on what I could try.

Thanks