Hello. I have a 2000 S10 Blazer, 4x4, vortec 4.3. 132k miles. As I was driving the other day, I noticed a strange metallic rattle coming from under the truck, near the front as best as I can tell. It was intermittent at first but seems to be occurring with greater frequency/severity. The rattle becomes faster as I accelerate, almost like if you were to hold a pencil against a bicycle wheel and spin it. Also noticed a bit of a "pop" when shifting into gear, although this is seemingly random as well. No terribly noticeable vibrations... inspected driveshafts, u-joints seem to be intact. I cannot reproduce the sound in park, at idle or higher rpms. Also doesn't seem to occur at highway speeds... only noticeable at low speeds with acceleration/load/going uphill/etc. No problems shifting... Any ideas? It is not exhaust/cat related....

 

Hi, glad to have you in the forums. Did you check to see if your catalytic converter is bad?
EDIT: DIDN'T SEE THAT YOU STATED IT WASN'T EXHAUST RELATED.

 

Check your front brakes, had a similar issue to your description about a month after I bought mine. Turnes out it was one of the brake pads sitting kinda sideways. I found this quick because when I got on the brakes the sound stopped. Good luck