RaiderMike67

Ok, was driving me crazy, certain songs with a certain bass we causing all kinds of what I thought was either distortion or a loose speaker. Checked out everything and the speaker is 100% tight as is the speaker cover, what I realized was that with the door open I didn't hear the vibrations but with the door closed I did and the only conclusion I came to was the lower panels on the outside of the door were vibrating with the door closed.

Any ideas on what I can do to stop this? How are those panels attached?

Hymie

If what you say is correct – having someone place their hands or other object in contact with the outside of the lower door panel should affect the vibration. Doing this would to some extent confirm your theory.

Many years ago, I added speakers to the front doors of my first car – along with a power-graphic equaliser. There was a marked reduction in speaker sensitivity with the front windows wound down, which would have reduced air volume behind the speaker (there was minimal clearance between the wound down window and the rear of the speaker coil).

If it really is an acoustic coupling causing the vibration, then any form of additional bracing/stiffening on the door panel should alter things (hopefully for the better). But you might have limited room between the door panel and the wound down window, to fit anything.