So... I posted most of this before but have some new info... while my 4Runner was parked it was hit from the rear, this damaged both lower control arms and the axle housing among other more cosmetic things. When I got the 4Runner back, I noticed a clunk... at first it was only upon deceleration, then it started when I accelerated as well. It seems to be coming from the middle or front of the undercarriage. It only happens when the roads are wet. It will happen regardless of whether or not it is in 4WD, the only absolute is that it happens when the roads are wet. The wetter the roads, the more pronounced the clunk.

My question to you: What the hell is it? It seems like the most random, obscure issue, I don't notice any performance or handling differences. I have limited mechanical experience, so if it's something I can check, great, if not don't be afraid to hurt my feelings and tell me to take it to a shop. Any and all help would be greatly appreciated, thank you in advance.

Also... this may or may not be related to the collision... the only reason I mentioned the collision is because I only noticed it after I got the vehicle back from the shop, let me know what you think.

 

Most likely your inner axle seals are allowing gear oil to leak into your rear drums which gums up brake dust and can give a clunk sound or if its not that, your driveshaft probably needs some lube.

 

Well, I got a clunk ever since I screwed with the panhard bar. I think its coming from your control arms or panhard bar. They shift from time to time.

 

could be a busted rear shock at the top. they rot out and the hit could have
been enough to bust it. but only when wet ?????????

 

https://www.yotatech.com/search.php?searchid=4368698