My iPhone 5 and Garmin nüvi 3597LMTHD create interference when phone calling on bluetooth car systems

I recently purchased a new Garmin nüvi 3597LMTHD. This device causes several interference issues with the in-car Bluetooth in my vehicle and several others that I have tried, with my iPhone 5 as well as my wife's iPhone 5.

I have my iPhone 5 paired via Bluetooth to my 3597 and also to my car (UConnect on my 2012 VW Routan). I use Live Traffic, so need the bluetooth connection for data. When I first made a phone call in my car, I told my iPhone to make the call through my UConnect; there was a lot of static though (on my end and also the receiver's end as she told me that she was having trouble hearing me). I also noticed that even though the call was happening through my car stereo (UConnect), the 3597 was showing the call on its display.

Afterwards, I tried making the call through the 3597 (by selecting the 3597 from my iPhone when I made the call). It started on the 3597, but had a lot of static & interference; same as on the UConnect. The 3597 then dropped the call and it was picked up by my UConnect - same static.

I went to apps and shut off the telephone over Bluetooth functionality on the 3597. This cleared up the problem of the phone calls showing up on the 3597 even when I was making them on my UConnect, but the static was still the same.

I tried resetting network settings on my iPhone 5; same problem. I then tried with my wife's iPhone 5 (with the Bluetooth on my iPhone shut off completely); same problem. I have also tried this 3597 with my iPhone 5 in multiple other vehicles with built-in Bluetooth (a couple of Fords with Microsoft SYNC and a Kia with built-in bluetooth - exact same interference issues.

When I disable the bluetooth connection between my iPhone 5 and the 3597 (only having a connection to my UConnect), there is no interference.

I previously owned several TomTom GPS devices; I was always paired to these via Bluetooth at the same time as my UConnect, and never had any interference issues of any sort.

I have tried unplugging the power cable from the 3597 and using only the 3597 unplugged (to see if it was the traffic antenna perhaps causing interference) - same issue. I have also tried moving the 3597 around the car to the top corners of the windshield and even the back seat to see if I could eliminate interference by moving the antennae from the 3597 and my UConnect apart; still the same problem.

I also previously owned a 3590 (in March 2013) and had the same issues reported above. I returned it at that time thinking that the soon-to-be released 3597 would have addressed those issues. Apparently not.

I have spoken to Garmin's customer service telephone agents twice about this, but neither was any help. They said they have reported the issue, but did not take my contact info or anything so they have no way of getting back to me about resolution. I then e-mailed Garmin tech support, and they said they have no solution.

Wondering if anybody has any suggestions?