soft "clack" sound at 40km/h
 

Anybody else hear this?

I encounter this every morning: I start a cold engine and I let it go through the warm up idle. Then when I drive off I hear a soft "clack" from the engine bay when the speedo crosses -40km/h (25mph). I don't hear the clack for the rest of the drive.

What is happening? Apologies if this has been discussed before.

I believe there is only one other thread on this, but you are not the only one. Its happening in both Auto and M/T cars. I'm not sure for you, but if the car sits off for 20-30 min and you drive off again it'll make the sound again. I plan on taking my car in to the dealer to check it out soon.
I assume this is the sound?

http://www.ft86club.com/forums/showthread.php?t=38684