Strange thing is, it possibly isn't there during the first half second of the call. I have not done anything to solve it yet, so I didn't make a custom ground for the radio, use chokes around the powercables, etc. Just wondering if this is a known issue with known solutions. The radio is an (old) JVC KD-AVX33 with build in bluetooth carkit with a Helix HXA-400 amp on the front speakers. All radio, USB, etc sources are whine-free.
