Well, im startin' to worry, this is the first time my blazer has done anything wierd (that wasn't my fault =D ).

Last night when I started it up, it was making this wierd whirring sound coming from under the hood. It sounds exactly like what 4wd sounds like when its engaged. I know its not the 4wd however because I put it into 4wd and I can hear both sounds.

It seems the sound is exactly relational to the speed, regardless of acceleration or breaking.

Any help would be great, thanks guys.

 

Could be one of the accessories on the front of the motor (alternator, water pump, A/C compressor, or power steering pump). Pop the hood and see if you can narrow it down to a particular location.

Also, take a look at the cruise and throttle cables. If they are resting on the PCV hose, you could be hearing the PCV valve rattle being transmitted through the cable into the cabin.

 

It kinda sounds like the sound is coming from underneath the brake fluid overflow. But who knows.

It kinda sounds like when you go in reverse real fast, but in my case, its all the time, even stopped. Also, the faster I go, the more high pitched it gets, then after about 15 mph it goes away (i assume because its too high pitched for me to hear it.)