Mmm ... well for the Bluetooth only modules, often referred to as ULF modules, manufactured by Visteon for BMW I think theres no so difference between USA and Europe version of this module. Theres only one part # regardless of country for these modules.

Infact I believe they are now only fitted at the factory for European cars with BT option (not telematics). USA cars only get the BT/Assist combo unit from Motorola as a factory option.

As far as your distortion problem ... perhaps you have a very early generation of the module. There was some issues with the first generation of these. Take a look here to find out which generation of module you have.

Visteon Bluetooth Module:
84 21 6 934 552 end of life 06/03 1st generation
84 21 6 938 610 end of life 10/03 2nd generation
84 21 6 934 961 end of life 03/04 3rd generation
84 21 6 950 089 end of life 06/04 4th generation
84 21 6 945 387 end of life 11/04 5th generation
84 21 6 955 522 end of life 04/05 6th generation
84 10 6 969 268 end of life 04/06 7th generation
84 21 6 958 358 end of life 05/06 8th generation
84 10 6 987 546 In production 9th generation