Just discovered that this is possibly the rattling noise I hear at 1200 - 1800 rpms. Is there any harm in just putting up with the noise or is this something
that requires an immediate fix? (it's a 4.3 in a 03 Blazer LS with 85000 miles)

 

Not sure, its a new one on me.

Taht being said.
The balance shaft has bearings at both ends, it attaches to the timing gear and if it locks up you could be looking at major engine damage if it takes a crank or cam with it. Could you take off the timing cover and see if its walking out, could it be yourcam shaft is walking around as well?

 

GM put out a TSB on this problem and maintains there are no durability issues associated with the noise. However, they have a kit available to fix it. From what I can tell it's been an ongoing problem with the 4.3 since 1999. Why they just don't fix at the factory remains a mystery. Since my original post I've learned the noise may or may not get worse and there's just minimal risk involved if I choose to live with it.

 

In that case, your call.

What's the fix?

 

Mine has done that for over a year I have tore the motor down myself as well as had a friend who is a GM mechanic look at it he said according to their system and their experience with it just leave it alone unless the noise keeps increasing and the vibration keeps getting worse. ( Like every week he said) So it depends on how loud it is I have heard one that was shot and you will never forget once you hear it will be a deep loud rattling noise and when it gets ready to go out its sound like a metal on metal scream. Like a lot of other post it is so hard to diagnois a problem that you can not visablely look ator hear for yourself that why we all work together everybody has different experiences and sometimeswe all may be wrong but heyits just my opinion but as long as its running and not continuing to get worse don't mess with it just keep and eye on it.