bluetooth garbled phone on my Nissan Altima

[marklyn]

I have a '07 Nissan Altima with the navigation system (bluetooth included). Prior to my HTC Diamond, I had a Palm Centro and the bluetooth worked really well with the car. I could make/receive calls and I heard the callers well and they heard me well.
Now, with my Diamond, I can make a call but the caller's voice sound very garbled. They cannot even hear my voice at all.
I've done the basic troubleshooting, repairing, etc. and all the research I've seen has been in car forums where the technical aspect isn't there like it might be here. This is an apparant problem with other people too.
There is a screwy 'workaround' that is difficult which involves switching a call from the nav system to the handset and then from the handset back to the nav system, but that is screwy and dangerous while driving.

I was hoping someone could maybe point me in a direction to start researching. I have two Diamond phones at my disposal and both have the same problem. One has stock Sprint ROM and the other has Juicy 3.0 ROM, but the problem is the same for both.

Would this likely be the bluetooth in my phone that might be at fault? Is there something I can possibly do by tweaking or upgrading or changing something about the BT on my Diamond?

Could use some ideas...