[Vwdiesel] cv joints ?

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My '81 diesel Caddy has an unusual sound.  It doesn't do it all the time but I want to know what it is if anyone has input on it.  When I first start out all is fine but after about 12-14 miles of stop-n-go city driving, there is a thump thump thump sound up front that increases with speed.  It has 125,000 actual miles and I've kep it in tip top condition.  Counld this be a CV joint going bad?  I also note that at slow first gear speeds on the expressway during rush hour riding in it feels as if the pavement has waves in it when it is actually quite flat.  I'm thinking about replacing both axle shaft shafts complete and with lifetime warranty - only $65 each side.  Thanks so much for your help!
 
Tom Norris
'81 Rabbit LS diesel
'81 Caddy diesel
'83 Caddy LS diesel
'03 Jetta wagon diesel
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