"I just bought a 2006 explorer. I used 4wd drive this morning in the snow. When i took it, it clunked very loudly when i backed up and then when I turned at the end of the road (right). It did this the second day i had it also, same situation. After driving it down the road, the noise has stopped. I can only assume it is related to the 4wd as it doesn’t do this at any other time Is this a normal thing?
Check the front halfshafts to see if either has a worn out CV-joint.
Tester
When you engage 4 wd, you bring into play two more cv joints. It is a rwd truck based chassis. If it does not do it in 2wd, you can eliminate the the main drive shaft. But, like a fwd car, it does have two cv joints which in newer models, always turn and wear. That and the shaft from the transfer case to the front differential would be my first look see. When was the last time the front differential and transfer case serviced ? If you have an electronic actuators , they can clunk loudly while trying to engage while turning and stopping or , I’m thinking to, if there were inadequate lubrication… I would have it serviced and have them look for excessive play when engaged and check to see if the actuators were working properly.
4WD does not like operating on pavement, even wet pavement, especially when turning or backing when turning. Save it for when you are driving on loose dirt, mud, or snow-packed roads, so the wheels can slip a little when you turn corners…Basically, you use 4-WD to get unstuck, not for driving around, even in bad weather. A little slush on the road is not reason to engage 4-WD…
What I think happen is when you engage the transfer case and then backed up, the transfer case went into 4 wheel mode. When push the button on the dash it does not go into 4 wheel dr right away. It can take a few feet for it to fully engage and when it does it can clunk loudly.
As others have said you should have all fluids checked and or changed.