front left door speaker vibrations and distortion

[hocky1]

I have seen and read the DIY for removal of the speaker and plastic cover. I have an agonizing problem with my front left door speaker. The whole plastic area surrounding the speaker vibrates and buzzes when very low notes are being played on radio/cassette/cd. The buzzing sound is really the whole front plastic cover vibrating within the very badly designed frame and holders which has only one screw at the bottom to anchor the whole thing and some side and bottom breakable plastic tags and hole. I have removed the cover and no more buzzing sound and it comes back again as soon as I put it back in. The speaker is 9 years old, but still looks very clean and good. The sound is more of low range/bass than mid range although the mid range still gets out with a struggle. Don't really want to change speakers due to the mess I will get into in the redrilling of holes and removing all the speakers.......there are 6 of the larger single cone ones(2 in the back shelf and one in each door) and 2 tweeters in the dash. None of the other door speakers has this vibration and buzzing sound. Does look like I will have to find some thin tape or something to insert between the main plastic frame lining in the door and the plastic speaker cover edges.
Should prevent all that vibrations making the buzzing sounds. The speaker is not damaged and seems like there's nothing behind the speaker causing this irritating sound.

Has anyone else had this experience in their Benzs? What have you done to stop the bothersome noise? I am pretty sure the speaker itself has not gone south? Thanks.

1994 Euro C180.