I'm sure the plastic engine covers are also to reduce engine noise. I have the oem cover on my alh tdi and i ran without it for a day. My wife even noted the louder engine sound inside the car.

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1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped