Is the best that I can define the sounds coming from the rear (springs mostly) that usually can be cured with water jets but only for a while. I have tried WD40, silicone in spray, the chassis clean up with a kind of parafine and nothing. Yestreday I close the range of possibilitis using a garden spray + water and definetely it was the leaves separator plastic area. But today is there again and is kind of shame to me to drive between other people with this old style bed disguised as a Blazer. I tried the search function but none had mention this type of sqweak.

Have all of you a nice 2008. Saludos a todos y a cada uno. Un abrazo desde Chile.

 

It sounds like you've located the problem and now just need the cure.
Maybe you could jack the truck up by the frame to allow the springs to hang and install some pieces of rubber ( like from an old tire tube) between the springs.
When you let the truck back down it should hold the rubber in place.