I'm wanting to use my N73 with the AD-15 to connect it to the line-in of my car stereo, the only problem is it's very quiet and if I turn the radio up to compensate a high pitched whistling can be hear, this dissapears if I remove the AD-15 from my phone. I've tried a N92 and that is a lot better, are there any firmware upgrades that fix/improve the audio output or is the N73 just not very
powerful?