In my experience, bad big ends make a knocking sound when the oil pressure light is on, very noticeable during a cold start. The other time they make a lot of noise is when you put your foot on the clutch during an upward gear change, you'll hear it knock as the engine decelerates before you engage the next gear.

In lesser engines, say an old small block chev, when you give them some big revs, the big end stretches out of shape which pinches the sides of the bearings into the crank causing the oil to be pinched out & then you get a metal to metal condition which means total big end failure is going to happen sometime soon.

In B20's, this just doesn't happen this side of 6000rpm & if you get hold of a B20A, you'll find the big ends are always nice & round.