I got a transfer case from Marlin with a 4.7 in it that did that. BAD. He replaced it. He told me later that the gear itself had a minor ding from shipping, and that was the cause. He dressed it with a diamond file, and it was good as new - in fact, he resold it as new, which it really was.
I just "QA'd" it for him.
That is exactly the kind of sound it made, only mine was REALLY bad. It was a very minor ding. You might take yours apart sometime Rudy.
However, I am noticing my R151 is really loud too, made worse by the fact that my shift tunnel cover is not anywhere close to sealed since the body lift. I asked Marlin about that, and he said the gears in the 151 are so big and heavy (first gear in particular) that there is just no way to make it quiet, nor shift like a sports car. The price you pay for toughness. I know you run a 151 also, Rudy, so it may in fact be the 151.
I aim to 'fix' mine by making a well-sealed shift tunnel cover. My original design has some bugs anyway. Hard to remove really. The shifter needs to be remade to clear everything a bit better, just gonna use some 1/2" rod or something and make it snaky.
Just keep an eye on the coupler, and the bearings. Wear items. Not horrendous to replace when the time comes.
