If it sound like a jet engine it's most likely the ball bearings in the heat sink fan that has or is in the process of dying (Under the assumption that it hasn't always sounded like a jet engine)
Ball bearings are a constantly moving part of the fine and what would take the most friction so it is the first to go, given this is a P4 it's most likely just reached the end of its life span
1st option
You can replace it with a factory/clone/refurbished replacement or find just a fan replacement that will fit the current heat sink
This will perform the same as when you first got the P4 so it should reduce the noise
2nd option
You can look into a non fan based heat sink; this would generate 0 noise and is popular with a "Silent PC" configuration
Most of these will work on either the inbuilt fans provided in the case to cool the heat sink or via heat transfer causing an upward draft if the PC has no fans
As a reminder as Journeyman pointed out "Product suggestions are explicitly off topic on this site" so if you do ask for product recommendations this question will likely be closed
pro tip: searching via your pin configuration rather then your CPU model will be the best way to find relevant products