most likely you need to remove the foam. the clearance between the stock grill and the speaker is minimal and when installing a good pair of speakers in there the height of the new speaker is going to be a problem to get inder the factory grill so by removing the foam it will give you a little extra room and it will not press on the aftermarket speaker inducing distortion. If you are worrind about rattles get some dynamat and line the back of the panel around the factory grill but do not run it to close to the hole or it will also take up the room you need for the aftermarket speaker hieght.
hope i helped