clicking noise sounds like transfer case

[bakerboys]

I have 85 k20 37 inch tires had driveshaft lengthend and rear gear 4.10 replaced it was making a bad grinding noise thats all good now Just put a 355 roller in it wow is she fast to be big BUT new problem every now and then I hear a taptaptaptaptaptaptap noise its not the engine

Sounds like it is coming from where my rear driveshaft goes in to transfer case does not do it all the time If i manually shift into 1st or second its there go back to drive its still there put it in nuetral and back to drive it goes away mostly does it when first taking off or taking off and turning at same time

trans th400
t/case 208
3/4 ton truck

thanks for your help