Noises problem
1998 BMW 323 6 cyl Two Wheel Drive Manual 88000 miles
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what is the unit that is in the left rear of the engine that is round and has a filter in it? this unit just started making a loud noise when the vehicle is first started it then shut off 2 minutes later. it never did this before. can you help me!

That unit is the secondary air injection pump. It injects air into the exhaust manifold on start-up before the coolant temperature reaches a pre-determined level to quicken the catalytic converter start-up. They do make a whining sound sometimes and it does not always mean it is failing. If you are considering replacement the part# is 11-72-1-744-490 and should be available online from several BMW parts suppliers. Realoem.com or BMWpartsonly.com or European auto source (714)369-8524 just to help you get started.