I have just got my Blazer back from having a transmission put in and they removed the catalytic converter, it was bad or something I dunno. And I drove it for 2 days and now I get this god awful grinding noise at low speed and high speed, not constant but every 6 to 15 seconds, it sounded like it was coming from my passenger rear but upon pulling into my driveway it sounded dead middle of the vehicle....Its loud and major! It is a HARD grind and kinda feels like it makes the truck move funny...Maybe thats just me but it isn't like one tiny grind its many put together one time and then it quits and then its maybe one big grind another 6-15 seconds. Anyone have any clue what this could be? Also I noticed that when I turn my heater on and then off it makes this huge whine noise or sounds kinda like an old man cough...lol That wasn't like that a few days ago either...The Check Engine light is on this morning, it seems to be getting way worse and I removed the tired to see if any rocks were stuck in the heat shield and nothing...so ????? This Blazer has given me one problem right after another, I've already put 6-7k into it this year alone. Im about done!

 

If they removed the catalytic converter and did not replace it, that is probably why the CEL is on.

Have you checked to make sure that the exhaust system isn't coming into contact with the driveshaft? Like when you hit a bump or turn just right...?

 

Would that make it a constant grind? Because this comes in intervals like every 6 seconds it grinds multiple times then another 10-15 seconds it grinds hard once...If it was coming into contact w/the driveshaft wouldn't it be a constant grind...I'm not smart with this kinda stuff so you could be right. Ty

 

I have seen weirder things. Something to check out.

 

You're going to have to isolate the source of the noise before anybody can tell you much more. Plus, what kind of reputable shop would remove a catalytic converter and not replace it, thereby violating Federal law?

 

I took it to a shop yesterday and the rear ends going out...great!!