* Faulty Fan Motor: The most probable cause. The fan motor bearings might be seizing up or wearing out, causing that loud screech/whine. When it gets up to operating speed briefly, the friction might be enough to jam it.
* Wiring/Relay Issues: A short circuit, faulty relay (which controls the fan's power), or a problem in the wiring harness could be causing the fan to run at full speed for a moment before the system shuts it down to prevent damage.
* Faulty Temperature Sensor: While less likely to cause the *jet-like* noise itself, a bad temperature sensor could be sending a false signal that makes the PCM (Powertrain Control Module) think the engine is overheating, triggering the fan to run briefly at full power.
* Loose Fan Blade: Less likely, but a loose blade could be causing a vibration and loud noise before it settles and stops the fan due to a safety mechanism.
What to do:
1. Don't ignore it: Continued running of the fan like this could damage the motor further, or even burn out the relay or wiring.
2. Safety First: Make sure the engine is OFF and cool before attempting any inspection.
3. Visual Inspection: Carefully inspect the cooling fan. Look for anything obviously loose, damaged, or out of place (bent blades, etc).
4. Listen Closely: If you can safely get close to the fan when it's making the noise (engine OFF, of course), listen carefully. Is the noise clearly coming from the fan motor itself, or is it more of a belt-related sound?
5. Professional Diagnosis: This is likely a job for a mechanic, especially if you're not comfortable working on your car's electrical system. A mechanic can properly diagnose the issue (testing the fan motor, relay, sensor, wiring), and get your Trailblazer back up and running reliably.
Ignoring this could lead to overheating issues which can cause serious engine damage. Get it checked out as soon as possible.
