I just fixed a very annoying engine vibration rattle in my CRD...I can still feel the engine vibration but the rattle/noise is now gone.
I found the inner seam where the quarter panel and the wiper grill panel are spot welded together were hitting the inner panel if there was enough vibration. You can test it by tapping the top middle of the quarter panel.
The two panels spot welded together can be seen here from the front, but they are supported well and dont tap the inner panel at the front despite being so close.
I have heard that dealers fix this by flexing the outer panel away but I chose to inset a strip of rubber to stop the contact.
I know you all are having snorkel noises but if this is also the problem...the noise is very annoying and very loud throught the entire firewall.
Matt.