Yes, the fuel pumps are loud; my '95 E420 is very noticeable - especially when in the garage and the sound reverberates off the walls. I've asked two different dealers and a couple indy's if that is normal - they've all given me that "get over it look". You can hear it from the cabin too, but just more of the high pitched generator-like sound. As you said, you really have to listen for it. I think the pumps are around $200 each & you need two, so I wouldn't worry about it until there is a mechanical breakdown.