Me too. I've been told oil pump as well. Same as tkamiya, g-benz, mine has done it since I've had it. It can be louder or quieter depending on the weight of oil I'm using and the outside temperature. I've found that more viscous oil (15W-40, for example) tends to be a bit quieter, but it's still there. Hasn't changed since I got it, and the stealership says either cough up $600 or so for 1 more minute of quiet, or leave it alone because it's just a noise and it's not gonna break.

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Brian
1995 E320 wagon