ok... after about 20-30 minutes of driving, my trucks front end is making a popping sound, only noticable from stop to about 30 mph. and usually doesnt happen when brakes applied. it really started after about a 45 minute drive in stop and go driving. and was felt in the floor on both sides and in the wheel. since then ive had the front end checked. and the plastic piece between the front axles replaced. nothing visually wrong with it. it hasnt been that bad since the last 45 minute drive. but its still doing it. it seams to be heat related, and its getting colder here. harder to get to act up. i had the front end checked at 2 different shops and both cant find anything. but thats cold too, not fully warmed up after a long drive. the truck has been sitting for about 4-5 weeks while headgasket was being done and it had a brake pull, changed the front calipers and lines and pads. pulls gone, but now it pops. almost sounds like somethings going to fall off! i cant hear it with the window down as all the noise from the engine and the exhaust. . im pulling my hair out! any helpful hints?