Well I finally went to the dealership to take a look at the left door rattle which happens only when the window is fully rolled up.
It was related to a loose regulator as others have also reported here on the forum. I'm glad I found this solution here on the Z forum before I went to the dealer. I was fully prepared for some BS since the dealership where I bought the car from had previously looked at this & thought it was caused by an after market door speaker upgrade being too large/deep & causing panel interference. I never really believed that explanation since my right door did not have any issues with the same size speaker inside.
I had replaced the speakers after being told this but one was torn anyways. My Pioneer HU really sounds great and is so much better sounding than the factory stereo that comes with the Base Z. I bought 6 & 1/2s but slight lower profile (TS-A1675R Pioneers) that fit just fine.
