Well this problem can be categorized into two ..
1. Mechanical failure
2. Motherboard failure.
1. Mechanical : Try to isolate which moving component inside the system is making noise ...i.e. Fans , optical drive , HDD or the shaky chasis.
Now to do and RCA (Root cause Analysis). Check for history and also check for any thunderstorm , lightning. Well you can also try to maually stop the power supply fan by inserting an objecxt while the system is powered DOWN !!! and then power ON to check for noise as this is one nasty fan that spoils the froth...
The same can be done for others.
2. Motherboard : This normally arises due to ageing and also due to some updates additionally required. Manufacturers normally provide update for them ... They are the mecca of solution to this problem..
BIOS FIRMWARE UPDATE.. very suitable for DELL Laptops and Desktops
I stumbled upon for DELL computers .. http://www.delliq.com/dell_bios_update
Kindly await as i dive to check for more , will keep you all posted and do lemme know whether this one helped !!!