I have a 2003 chevy blazer, and when i put it in four wheel drive it makes a humming noise. It seems to start making the noise as soon as it shifts into second gear, and quit after shifting into third. Only does this i four wheel.

Is it common to have a little humming noise in four wheel?

Also, will a check four wheel drive light come on, if my transfer case needs fluid?

 

A little noise is going to happen because of the parts in the transfer case are working. I don't think it's a problem...

 

Same thing happens in my 92 jimmy the transfer case starts to whine at about 35mph, and when i get to about 40-45 mph its gone. or if it shifts into overdrive at 35 it goes away.im guessing its normal.

 

Well the humming noise seems to be normal. However, i didnt know if my transfer case has ever been changed or added to. So i did a transfer case fluid change. Thank God i did, i took out maybe a cup full of the nastiest fluid i have ever seen. Instead of the fluid being red it was almost a brighter orange color... Stuff was bad!

 

Change/check fluid in front diff as well. Just as important for 4x4 as your TC.
Blazers are somewhat notorious for slow leaks out of the front diff.

But, as said, correctly, there will always be some extra noise/hum with the additional moving parts when 4x4 is engaged.

Good luck!