1994 4wd makes whining sound
 

I have been having problems with my 4wd lately. I start to drive and everything is good til everything starts to warm up and once I hit 50+ mph my 4wd starts to make a horrible whining sound until i engage 4-hi. It doesnt do it at any point before 50 mph. Everything engages and disengages just fine but worries me i am messing up my transfer case by having to engage 4-hi while im driving. Any ideas?

no verdicts yet?