Is This Normal?

Hi TacomaWorld,

Thanks to all the knowledgeable contributors for your help so far in my first month of owning my 2002 XtraCab 2WD MT. What a fantastic vehicle!

I'm trying to diagnose a clunking sound that occurs when I quickly release the clutch with high RPMs, such as during downshifting or when revving between shifts. The sound is coming from beneath me and sounds like metal on metal. I've had the mechanic check under the vehicle, but nothing appears to be loose.

However, there is one bolt in the picture (near the transmission output shaft) that I'm unsure about. I can't find any information on it in the service manual. To my eye, it looks loose, but won't tighten (as shown by the vice grip marks). When I shake the driveshaft, the pin also shakes back and forth (as shown in the video).

Could anyone provide any thoughts or insights on this issue? Any help would be greatly appreciated.