GM Service Manual Online
For 1990-2009 cars only

Cause

Correction

DEFINITION: Knocking or clunking noise occurs when operating the vehicle in high gear or coasting in NEUTRAL at 16 km/h (10 mph).

Loose flex plate bolts or a damaged flex plate

A flex plate that is cracked or has loose retaining bolts may create a clicking, clanking, or snapping type noise in the transmission housing.