My Crossfire Coupe 2005 auto, which I've had since 2008, has started making loud fluting noises when driven from cold. The colder the weather the louder it flutes, particularly on acceleration. Pitch changes with each gear change. Noise lessens as engine warms and disappears altogether at normal running temperature. Car drives normally, whether fluting or not, and does not make the noise when idling. Our local mechanic serviced the blower fan, which had started to fail intermittently and suspected as the source of the noise, to no avail. Two recent events in the summer may be relevant: 1. the prop shaft bearings were replaced; 2. I stopped briefly on one occasion and was unable to restart - nothing at all happend when I turned the key. Never happed before. After an hour or so it suddenly started normally.

Any ideas what is causing the fluting noise? My mechanic has spent some time on it but can't yet figure it out.