Thumping Noise Under Dash

[ntp888]

I have a 2000 ls 400 with 120,000 miles on it. I have a thumping noise that sounds like it is coming from under the driver dash or bottom of firewall floor. It only occurs when I drive over bumps and the wheels are turned. Even riding over my lawn will cause it. I took it to a shop and replaced the struts and caps but to my displeasure the noise is still there. $600.00 out the window. Anyone else have this problem?

[RDM]

It's a long shot, but worth checking. My 1992 had a rattle similar to something loose in the glovebox, but louder. I chased it down for over a week and finally found that the passenger side wheel well liner was loose. It's secured with screws that run into plastic anchors that snap into the body of the car, one of those anchors had pulled out so it was flapping over bumps or at speeds, seems impossible but that little piece of plastic hitting the body can cause just the right resonance to sound louder and more solid. I used silicone to secure it better and haven't heard a thing since.

[ntp888]

It's a long shot, but worth checking. My 1992 had a rattle similar to something loose in the glovebox, but louder. I chased it down for over a week and finally found that the passenger side wheel well liner was loose. It's secured with screws that run into plastic anchors that snap into the body of the car, one of those anchors had pulled out so it was flapping over bumps or at speeds, seems impossible but that little piece of plastic hitting the body can cause just the right resonance to sound louder and more solid. I used silicone to secure it better and haven't heard a thing since.

[ntp888]

thanks for the suggestion. Checked it out and it seems to be secure.