I assume you still have the full factory warranty, that said, keep your loaner until they fix your car to your satisfaction.

I took my 93 Mercedes to the dealer to have a window gasket installed and a detail. I wasn't satisfied with the detail job so I left the car there and drove back home with their 2015 e class loaner. I kept it for almost 3 weeks.

You are the customer, ie. The reason they are in business. Keep the loaner keys in your pocket until you drive your car around the block and are satisfied with the way it sounds.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2