'05 Legacy 4EAT automatic with 114k miles. Car is new to me as of earlier this year and I noticed a slight whistle/howling noise from the front diff while cruising at 60mph. Goes away if I decelerate or accelerate. Only makes the noise in that "sweet spot" of maintaining constant speed on flat ground. Sometimes it's louder or quieter and I have yet to determine if temperature has anything to do with it. Fluid seemed to be in good, clean shape with nothing of concern on the magnetic drain plug. Just the usual black/gray sludge you'd usually find on any diff with some miles on it. Ring and pinion also look good verified with a borescope stuck down the dipstick hole and drain plug. No weird wear pattern or chipped teeth. Everything visually looks perfect. I'm guessing the pinion bearing is the problem here. Not a particularly easy thing to replace on these and I'm guessing I've got some time on it. It hasn't really worsened in the 3000 miles I've put on the car. I just want to quiet it down a bit. I refilled with a conventional 75w-90 but I'm wondering if there's something I can add that will help. I know bandaids are just bandaids. I'll get around to fixing it one day but that may not be for another year or two. The noise is a bit annoying on extended drives.