Is it typical for new fuel pumps to be loud until they break in? I just installed two new Bosh replacments in my '91 300E alsong with a filter and they seem much more powerful than what I had in there before. Now the car starts with more authority. However, when I sit at idle, I can hear the humming noise they make. Do I need to insulate these with some thin foam from where the cover goes over them and where they contact the top? The old ones were weak but you didn't hear them at idle. Also, these are a bit larger even though they matched up to replacement specs on several websites.