I have a 2001 OB Limited 4EAT sedan, 70K miles, that started to make a whining noise at speeds of 40 and up. It sounds like it's coming from the front, and gets a little worse on acceleration. I took it to the dealer to check it out. According to the service report, "Tech found that noise is coming from the front differential area at higher speeds. Tech checked oil and found that it is at an OK level, a little thin, and very clean. Tech notes that front differential must be disassembled to investigate further."

 

I had the 60K service done a little ahead of schedule so I could complain about piston slap and ended up with a new short block. So some questions:

• if they used the wrong oil, could this have damaged something to cause the whine?
  
• could they have done something during the engine work to affect the differential?
  
• 10-12 hours to disassemble the front diff to find out exactly what the problem is - is this reasonable?
  
• how much trouble would I be in if I don't do anything about it? It doesn't seem to be getting any worse.
  

I would try a new and possibly heavier oil in the diff. If that changes the sound then at least you know where it is coming from. Changing an engine should not affect the diff, but sometimes I am amazed what folks can screw up.