strange 560sl sound

my 1989 560sl makes a strange squeeling sound only when starting cold. it goes away in about 2 or 3 minutes. sounds sort of like a fanbelt but more metallic. one mechanic implies it is air being pumped into the emission controll system but this doesn't sound right. its a pretty aggravating sound in a closed garage. any help would be much appreciated.thanks

[BrianR]

In a closed garage, you won't have to worry about the sound for a long period of time!