Hmm, thats wierd...family of squirels in your gas tank? they dont like the temp past 30?...lol...im pretty sure that this is a thing where in order to see what is going on with it you need to be there to experience it. Maybe it's something in your trunk? No, im sure you've checked that already (could be an unsecure spare tire or jack...but it has nothing to do with temperature.....this is a confusing question... never heard of it before) I have never heard of a clunking coming from the rear when the temp goes below 30. Why don't you have your mechanic sit next to you and let him see what is going on first hand?

 

Maybe you have water in one of your back tires? Its a thought but theoretically it could happen. I remember i had water in the back of one of my atv tires so when i took it for a spin in winter it completely threw it off balance and it was vibrating and shaking everywhere. Temp goes to 30, water starts to freeze and when it moves the ice around, it creates a clunking because its moving around in there and when you get up to speed it stops because of centrifugal force? Even when the temp gets up to 40 or 50 things start to turn back into water and clunking disappears? Its completely out there but if you could pinpoint which side of the vehicle the noise is coming from and remove one of the tires and shake it around to see if there is anything inside there? Maybe, im just throwing things out there for you to consider.

 

oh, today I sprayed the ends of the strut bar with WD40, and the sound was not there. but i m not sure if it is connected with the temp today. i've already checked my trunk for loose objects, everything is fine. my mechanic already heard the sound. he said the strut bar is the culprit. but i need to get another opinion from another mechanic and from you guys. whats your email add, i recorded the sound a couple of days ago, i'll send you the file.

 

Sounds like your mechanic sucks.

 

My email? pretty simple dr_talon@hotmail.com Yea, if i listen to it i would probably know what it is.