Ok so ill try to be quick and not have a big long storey here...
I went mudding for about 20 minutes after mudding i have a rattling/jingling noise coming from under/rear of the blazer.
By the way its a 2001 blazer 2 dr auto....And i also got all the mud off and from everywhere ....

First it was very loud only when im at a complete stop and then hit the gas then the noise would stop after i go over 20km's

Then noticed the noise basicly went away for a day and now its back but not the loud and say if im diving doing 30km's and pressing the gas i hear the noise but when i let off the gas the noise is gone and then if i push on the gas u hear the noise untill u let off the gas....

I had my ujoints checked and was told they look good...
Had my rear breaks checked also and was told they are a little worn but still good...

So if anyone could try and give me some things to check or maybe if someone had this problem befor...
Btw i checked the search and couldnt find nothing to this kind of issue

 

Let the truck cool completely. Start it up and crawl underneath the truck, grabbing a hold of the heat shields for the truck to see if it is one of them. I bet you broke loose a heat shield while you were muddin'.

 

So had a friend check it out he said it looks all good....
This noise was gone for the whole day yesterday then i was sittin at a red light and went to turn and then i heard it very softly lol

 

Heat shields can be tricky. You may want to tap them with a metal hammer to get them vibrating. Anything that continues to vibrate (after the initial "ding") is not proper. Some problems may be more noticeable when the exhaust is hot. Just be careful.

 

Well had him under there checking he said its good tight like his....
Noticed today while driving if im just coasting theres NO noise but if i press the gas a bit i hear the noise and had the wondows down it kinda sound like the front now lol....

 

It's possible that your catalytic converter is bad......my blazer was doing the same thing and it turned out to be the converter. Best way to tell is when your engine is cool, climb under it and try to hit the converter pretty hard and if you hear something roll around or something, then you know that's the problem.

 

uhhh, if you hit your cat hard enough, you can CAUSE stuff to break off the ceramic catalyst and then rattle around ... PROTIP: don't smack your converter. if it's bad, your O2 sensors will tell you, no question.

 

well, i didn't mean to hit it hard, just hit it and if there's something rolling around at a slight hit, then you know it's bad.