[Richls3rd]

Im not 100% where I would put this so here it is. Within the past 3 months or so my 2003 Chevy Trailblazer 4.2L has been experiencing some issues. Occasionally on ignition and sometimes randomly while driving the engine fan gets extremely loud. Like ridiculously loud and it just appears for awhile then goes back to being quiet again. Another thing is that my engine has a knocking sound that comes from it occasionally. Both of these issues are random but it seems they happen at least once a day. Thanks for the help!

 

[vipergg]

noise

Sounds like a fan clutch issue. You may have to change it, may think about doing waterpump if you have a lot of miles on it.

 

[SnomanAndASwede]

I had the same sound start occurring when gassing it. After checking the pulleys with the belt off I chose to replace the water pump (<$40) and the fan quieted down saving me some cash. Its been 6mo.s (only about 5k miles though) and no more crazy fan noise. They are connected together and one can/will cause the other to fail.:m2:

 

[Dmanns67]

I had the same issue about 3 months ago. I also had a winding noise as well. I ended up replacing the fan clutch as well as the idler pulley. Idler pulley was the cause of the winding noise.