Grinding Noise Under By Air Filter

[electro452]

I have a 2000 Buick Century. This past week I've noticed a grinding noise when the engine is first started in the morning . The engine is cold and the vehicle is at higher RPM's( choke engaged). The sound is coming from, what sounds like, under the air filter housing. The noise comletely goes away once the choke, idle, rpm's return to regular idling speed. This only happens when it's first started up in the morning and doesn't reocur when driving. I removed the air filter housing and the only item I can see in that area is the air conditioner cyclinder part ( don't know what it's called). Could the high vacuum that occurs when the vehicle is cold be causing a issue with this part or can it be something else I'm not thinking of ?