Update: Steve, you were spot on. I ordered and installed SPEC-USA PA12BMW kit. It works. No static, clicks, hum, etc. This unit clearly is grounded and handles the pre-wired trunk wires flawlessly. Keep in mind, I too tried the DICE and GROM units. Both did not work. The DICE unit was slow to recognize the command from the head unit and the static was present all the time. Finally, I have a solution. Having said this, I do think a handful of BMW's may have a unique issue that ends up creating the ground static you hear when trying to play music on the IPOD. Or, as you suggest, the other units don't handle ground properly. Regardless, the SPEC unit works. The sound doesn't sound as deep and crisp as the GROM unit, but that may be the settings on the IPOD or my factory head unit. I have some additional set up to run through. It's just sitting in my truck currently and I may leave it there.
As for sound quality, it is unfair to compare the SPEC unit to the DICE unit, since I never got past the static and clicks as I switched to each track and the constant hum when I played a song. You really noticed it during quiet jazz music. I do think it may be unique for us since there are so many favorable posts about DICE operating without a hitch. It just wasn't the case for me, and to figure this out was frustrating. I still can't imagine having to click battery cables as a solution. The supplier should focus on the grounding issue and offer solutions to try to ground the unit properly for the few customers that experience this issue as you and others like us reported.
Just an update on the DICE saga. I returned it obviously. I had to ship the unit back to DICE, not where I purchased it. DICE alerts the vendor when the unit arrives and the seller, issues credit. I received credit for the DICE unit, which was shipped by FedEd to CA. Unfortunately, I had to return the great ashtray docking unit to the original store too. Yes, I did like the tailored finish of the docking unit. It looked like it was factory option. It has been over a week now and despite tracking report showing it arrived in GA, I still have not received a credit for returning the item. I expect to sort this out, but it is disappointing. The company has been responding, by reporting it could take a couple of weeks. This seems like an excessive time. All in all. Lesson learned. I wished I came across your post and Delmarco's post earlier. I would have been fine.
Incidentally, I do have the Grom unit and 15 foot IPOD cord for sale....