Knocking or vibration while starting or turning engine off.
Vibration at idle (assuming balance shafts are properly aligned). Vibration will usually decrease noticeably or disappear when engine rpm is increased to around 1500 rpm.
Visual inspection reveals cracking, gouging, or peeling of the rubber in the mounts. Excessive wear may also rupture the mount resulting is fluid leak from the mount.
When the mount is removed from the car, the height between bearing surfaces is less than 65mm. The spec for a new mount is 70+/- 1 mm.
The height between bearing surfaces on an installed mount should not be less than 60 mm.
Tip from the 944 FAQ - The height of an installed mount may be checked by bending a heavy piece of wire into a " [ " shape with the points 60 mm apart. Use the wire to measure the height of the motor mount between the load bearing surfaces. If the height is less than 60 mm, the mount should be replaced.