LS430black

I just bought an 04 LS430 (Gulf Specs), really pleased with the quality, everything runs just fine, except the parking sensors. My situation now is that the 6 sensors in front will not beep when going near an object although they still appear in the Nav screen. I've reseted the system for 3-4 times, it did beep when it was turned back on, but nothing's changed. I've also checked the "Lexus Park Assist" menu and tested the beep (from 1 ->5) and everything was fine. My rear sensors are running well, they beep together with the back - up camera. Has anyone experienced this? I think the front buzzer has gone bad.