What you might be hearing is slip yoke knock.
http://www.agcoauto.com/content/news/p2_articleid/144
GM trucks of your vintage are known for this noise.
Tester
What you might be hearing is slip yoke knock.
http://www.agcoauto.com/content/news/p2_articleid/144
GM trucks of your vintage are known for this noise.
Tester