i have a 2003 super cab 4x4 (electronic select) with the 4.6L, about 52,000km on it. ever since i got the truck last year at 38,000 when i start it, it fires up normally and about 2 seconds after the engine has started there is a quiet clunk sound, i can feel it slightly, and the headlights flick dim for a split second when it happens, and then everything is cool. is this normal? and what is it? i was wondering if it's something to do with the 4X4 or transfer case, or maybe a solenoid of some sort under the hood. any ideas?

 

Sounds like maybe your air conditioner compressor cycling on? I know if it is sticky it will pull a load and dim the lights. I am no expert by any means but it kind of sounds like that is a starting point.