Noise in transmission

[andrew franic]

C180 classic, 02 reg - rummbling noise at 50 to 70mph. Had this growing problem for the last 3 months and can't figure out where the problem is. Front wheel barings and brake disc have been changes, Rear left wheel bearing changed, differential stripped down and re-done. then a shunt has started on take off and on slowing to a stop. Gear box oil flushed out 3 times but still the rumble is there and the shunt, although went away for a day or 2 is back (quite a kick sometimes)

Any suggestions as to the cause

 

[Ron Palfrey]

Prop shaft?

 

[television]

As Ron, propshaft