06 H3 with 140K miles. When I accelerate from a stop, the engine roars, sounding like a semi truck. Also, when driving at highway speeds, if the engine downshifts to climb a hill or when passing another vehicle, the engine roars. Sometimes I am able to power through the sound and it will go away but that often requires that I stay hard on the gas and keep the RPM's over 3000. Other times, when attempting to power through the roaring sound, I will hear a hissing sound when the RPM's push 4-5000. Anyone had this problem, and how was it fixed. I'm not kidding when I say that the roaring sound is EXTREMELY LOUD, not to mention that my MPG's fall off significantly when this occurs. I've heard effort that it could be the engine fan, but with the fan disengaged, the roar continues.

 

Exactly my problem but I don't know what causes it. It seems like it needs more power but the more I pressed on the gas the louder the screeching sound.............ANYBODY???

 

sounds like a typical I5 engine. When you run that high rpms, that motor gets loud. I know I have an 06, and when I need to get up a hill the noise is slightly obnoxious. Mine has plenty of aftermarket parts from front to back, but the big heavy wheel and tire combo keeps mine running slow on the uphill.

 

The sound is definitely not normal and there is a discernible difference from that and when it is running fine. It's not an all of the time problem, but most of the time. Yesterday, the truck ran perfectly and the ride was whisper quiet. Also, didn't mention before but it's an auto trans. I'm going to look into an exhaust leak as I have began to notice a strong odor in the cab. I've read that an emissions leak anywhere from the engine manifold to the muffler can cause the same symptoms. Here's hoping for some relief because this issue is very aggravating!

 

Rayo, I haven't noticed a screeching sound. Mine is more like when a semi truck is taking off from a stopped position and the engine sounds like it's working extremely hard but it's barely moving, with a loud blowing sound.

 

You have a faulty fan clutch that will not always disengage.

http://schwarttzy.com/wp-content/upl...ne-Cooling.pdf

 

Makes sense citiboy. I had AC work done over the summer and the clutch was replaced. The tech said that I would hear the fan noise. I'm no vehicle expert but it seems that in cold temps, the fan would not have to do as much work to cool the engine, right?

 

It should only engage momentarily on start-up and when the engine is hot. Did the tech replaced the fan clutch with oem? I think the newly installed fan clutch is defective.

Here's a little troubleshooting for 'ya. Goodluck.

Hummer Workshop Manuals > H3 L5-3.7L (2007) > Engine, Cooling and Exhaust > Cooling System > Radiator Cooling Fan > Fan Clutch > Component Information > Testing and Inspection

 

Thanks man, that should do it.

 

X2 on the clutch fan engaging. Heck it may be engaged all the time and that would rob power from the I5.