I noticed the front pinion seal has a small leak, did some research and found the axle crossmember bushing was shot, replace bushing and same time replace front diff fluid. Oil was black and nasty looking, I replace all the drive line fluids about a year and a half ago. also did the rear to compare and rear look like new. always use synthetic. now I have a very noticeable whine from the front axle. changed the fluid again about 3 weeks later and oil was black. There is small amount of fine metal on the drain plug, pulled the diff cover and ring and pinion look good no funky wearing. Still need to do the pinion seal. Any recommendation are where to look next. The whine is more noticeable at higher speeds and only when on the gas. If I just coast the all quiet. on a 2007 h3 about 145,000 miles.

 

Pinion bearing

 

Sounds like the front diff to me too.

 

How low was the fluid level when you looked into the leak? If it got low, it caused damage by failing to lubricate everything all the time.... ie Pinion bearing can wear and become slightly out of alignment or proper depth related to the ring gear. Causes whining under load at all speeds as the Pinion bearings turn much faster than the ring.

 

I don't belief the fluid was ever that low. there was nothing ever leaking on the ground, just look a little wet around the pinion seal. Pinion bearing would make sense.

 

Bearings whine at all speeds, gets louder as you go faster. If noise goes away coasting, you have bigger problems internal. There is a cheap diagnostic tool out there:

https://www.harborfreight.com/mechanics-stethoscope-63691.html?cid=paid_google *PLA+-+All+Products All+Products 63691&utm_source=google&utm_medium=cpc&mkwid=sROYl dmlw pcrid 327822404853 pkw pmt pdv c slid product 63691 &pgrid=71439424048&ptaid=pla-296227501885&pcid=1688396772&gclid=EAIaIQobChMI4uD upqT24QIVQQOGCh3IagxkEAQYASABEgLrjfD_BwE

Lift the vehicle and properly secure. Put in drive and check next to all moving points with a stethoscope until you hear that loud annoying noise. GL

 

Not just the quantity of fluid, but the quality of fluid is what's important. You stated: "metal" & "black fluid" noted on 2 occasions. You could be looking at a diff. change soon?