Vintage Cars: W114 1970 Transmissions ticking sound, speedometer cable, mercedes w114

Question
I have a 1970 Mercedes W114 with a automatic transmission. One day while driving, the car stalled with for no apparent reason at approx. 40 mph. I pulled over, started the car and noticed a new  ticking sound coming from the transmission area.  The ticking sound starts while in drive and continues through 25 mph when it begins to diminish. I appreciate any insight you can offer.  Thanks Mike.

Answer
may just be coincidental
may be a speedometer cable, possibly a leak in the vacuum, but doubt that . Could also exhaust metal that as it heats up ,expands and  ticks, then hot it goes away.
Has the stall hapened again?
and your sure its not coming from the engine - such as a valve tap noise??
Oh and check your flex disks forward and aft, they can tick and can do as you describe, would not be related to stall