Hi, I am new to the site. I just got back from Iraq in april and I bought a 2002 Trailblazer LS 4x4 a couple days after I bought it I noticed a knocking sound comeing from the engine. I dont know if it was there before I bought it or if it just started but that is when I noticed it. When I first start the engine you can hear it louder and it softens up some after it is warmed up but never goes away. When going down the highway I cant hear it unless I am stopped. That has been about 4 months ago and I have put about 7000 miles on it and that included about 8 trips that were 600 miles or longer. I have been able to pull a 6 x 12 Uhaul trailer loaded with furnature and a bass boat with no problems. I took it to a dealership and they could not figure out what the sound was without breaking down the engine and I would not let them do that because I didnt have the money. They did tell me that it sounded like it was coming from the lower half of the engine. Can anyone help me out?