I'm assuming you are under warranty.

Take it to the dealer and use their loaner while they figure out whats wrong.
Low coolant, water pump, loose belt, coolant leak, ....could be any of those things?

Good luck

Yelcoman

2006 G35 6 Speed Manual Premium Package A Factory Sirius Radio 110,930 miles, New brakes @ 85k miles, new 2nd replacement set Bridgestone Turanza tires @99930 miles, New plugs @106.7k miles. No mods required, I love her the way she came. Mod money goes to 401K. Regular 87 Octane, all the time.
Last fillup 3/8/10 23.79 MPG @ $2.49 gal with regular 87 octane.

You need to figure out of the noise is directly related to the engine rpms(1) or the noise of the fans running(2).

(1)check the belts and drive pulleys
(2)determine if the noise is the fans running at high or the low speed.

If 2 is more like what you have. Then the problem could be much more involved. An underperforming cooling system could destroy your engine before you get a chance to figure it out.

Several things can cause the fans to come on you will need to check before anything.
First off check the AC compressor to see if the inside of the pulley is spinning with the climate control off.
If that checks out you will need to check to make sure any of the following are not the cause.
-DTC- other than an engine over temp.
-ECM- when in failsafe due to certain DTCs the fans will run
-Coolant Temperature Sensors- DTC
-IPDM- the box located behind the battery also defaults to a fan ON when in failsafe mode.

This may be something for the pros as there are many things that may cause this type of issue and unless they can be narrowed down slightly more than a noise complaint.

-------------------------------- Nissan Sport Magazine