Looking at the HP Support page for Software & Driver Downloads, I don't see any audio drivers listed, for ANY of the Windows operating systems,http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?os=4063&lc=en&cc=us&dlc=en&sw_lang=&product=4329389
Driver: Small piece of software that allows the Operating System to communicate with a device
The device is the audio (Sound) chipset.
Do not know what the O/S is.
You have corrupted audio drivers.
What leads me to this conclusion is you have noise on your computer speakers, AND monitor speakers.
If it were just computer speakers, per se, I would say they are bad.
Or if it were just the monitor speakers.
Since there are no audio drivers listed, this means to me you need to obtain the Restoration Disk; if you do not have it.
(And I mean disk IN hand; not download from the internet)
Using the USA as an example;
The disk is free. The shipping and handling is not.
$17 for a 5 to 7 day ship; $24 for a 2 to 3 day ship.
Call 800-474-6836, 24 hrs a day, 7 days a week.
Have the Serial Number written down, to give to the nice representative. This is found in the white Service Tag, on the back of the computer.
S/N = Serial Number
For other countries use HP Support Worldwide,http://welcome.hp.com/country/w1/en/support.html
Install the disk in your optical drive.
When asked choose - Repair. (Non-Destructive Installation)