Hate to drum up such an old thread - sorry in advance. I got a BX2620 that's made this exact noise since new - 110 hours on the dock now. This still bothers me! I had it to the dealer and they claim they couldn't replicate it and the terrain was so flat i couldn't replicate either. Anyhow - still got the noise even in low range and pushing into a gravel pile or dragging.
I've checked the wheels, boot on driveshaft, ran without loader - sigh. Anyone ever hear of a resolution?