I've been in Rattle hell also with my Dash for 6 months.
Went to the dealer 3 times with it. This last week they had it for 3 days and said that the Speaker grill mount or something was flexing. They ordered a part and replaced it.
Drove it home and it was great!
Drove it to lunch and I heard it but seemed like it was 80% fixed.
Today I went out and it was a bad as ever . SO PISSED!!
You hear it most when turning left or right up a drive way. The weirdest nasty creaking sound.
Gonna give them hell on Monday!