Sounds like a mechanical failure - perhaps a cooling fan bearing.
So we can look up the system details what is the Service Tag number on the Dell sticker?
Do this so we can determine the video configuration:
Click Start, Run and in the box enter:
Click OK, and when the System Summary info appears, click Edit, Select All (Ctrl-A), Copy (Ctrl-C) and then paste (Ctrl-V) the information back here in your next reply.
For video device and driver information, expand the Components, click Display, click Edit, Select All, Copy and then paste the information back here.
There will be some personal information (like System Name and User Name), and whatever appears to be private information to you, just delete it from the pasted information.
With the unit powered off and physically unplugged from power remove the side cover to reveal the insides, plug in power, power up, reproduce the problem.
If the unit has external speakers, unplug them so you will have no sound and if there is still the same sound it can't be the speakers video/audio since the speakers are not plugged in.
Cooling fans could be present in the PSU (Power Supply Unit), one in the case itself for ventilation, one on the CPU itself, perhaps one on the video component, a fan on a third party video card that has been added, something else.
It might even be a defective CD/DVD drive (remove and media so it is not spinning).
With your listening ears on (as Judge Judy would say) and perhaps the tube mentioned pinpoint the afflicted/suspicious fan.
Click this link to read about other ideas from the Dell community and other places - even a BIOS update that has worked for some of those units:
Edited by joseibarra, 15 June 2018 - 11:06 PM.