I hope this is not the problem, but...
A bearing knock at the beginning will not make any or little noise at no engine load. It is when you load the engine or higher rpm that it starts to make noise. Has your oil pressure changed any at idle? If so, you may want to consider a tear down before more serious damage is done.
1969 Chevelle 460, 3.73 posi
Auto Gear Super Case with M22 gears
12.11 @108 mph
Top speed 114.23