...in a laptop. The fans in Laptops, continually alter speeds to combat heat build up and help prolong battery time. So one laptop which is doing lots of tasks might heat up and the fan(s) may speed up, and another litteraly idling (doing nothing useful, or strenuous) may have it's fans slow down to a complete stop.
So two similar laptops may not produce the same levels of noise. Even how the laptop sits can affect heat build up in the base. Make sure your's is sitting with enough ventilation underneath.
As far as knowing when fans are "going bad" there are loads of applications out there to keep an eye on onboard fan speeds ("Speedfan" being the most obvious one) but these need specific hardware support in the form of specialised chips on the motherboard. Check your own Compaq documentation, as often they'll already have some form of utility to check temperatures of CPU's and fan speeds.
Also, just searched on : Compaq nx9010 fan speeds
....and found these two links, among many (searching's a wonderful thing!).
I have a Compaq nx9010 Laptop with a P4 3.06 Ghz Procossor. I noticed that somebody with the same laptop has fans that sound totally different than mine. Can somebody tell me how to know if my fans are going bad.