Engine Builders: There have been reports that some 1999-2001 GM 2.2L VIN 4 engines tend to generate a droning noise that is especially noticeable at approximately 950 rpm after cold start up.
GM has identified the source as a natural resonant vibration of the air conditioning alternator drive belt. A revised belt, p/n 12575450, made of a different material may reduce or eliminate the noise.
Engine Builders: The AERA Technical Committee offers the following cylinder head gasket and cylinder liner protrusion caution on 1958-