My 2005 Tucson Crdi Auto has developed a strange vibration underneath when climbing small hills around town ? Dead quiet and smooth on the level but it starts as soon as I start climbing. 3000 revs at 20 to 30 KPH up our local small hils. Feels like the propshaft needs balancing? Recently been on a 2000k trip over bad roads and passes in the Western Cape with bad corrigated gravel roads. Could this have worked something loose?

 

No one got any ideas?