2006 CRV AWD 148k miles automatic. Only when accelerating up until it reaches 4th gear. Does not do it in park or neutral while reving the engine. Its not too loud but definelty can hear it. I've researched and seen it could be the transfer gear , a race/bearing on the driver side of trans behind some cover , a pinion bearing , or needs a fluid change which I'll be doing today with DW-1 Fluid as well as Hondas Dual Pump Fluid for the rear diff. I just bought this yesterday . I checked the color of the trans fluid and it was between a faint red and a grey ish color like used fluid usually is.