Strange antenna noise. Help needed

Hello folks. I have a strange noise problem with my headunit. I have a Pioneer X1 (The eu version of N1) and everything works fine except the radio. The signal is weak and if for eaxmple a motorcycle passes by I can hear his engine noise (spark plugs noise) in my Radio. The signal of the stations is weak and with many interferences. I have tried to change the antenna wire without any luck. I had this kind of problem before with Pioneer headunits in the same type of car , Mitsubishi but now this is pissing me off.... Any ideea where is it the noise coming from and how can I get rid of it ? I have tried with an older jeadunit from Kenwood and the noise was not there. I took the Pioneer at the store , they pluged in the power and antenna and the signal was damn clear so it musy be something in the car. Any ideeas ? Damn cold here ...

Try upgrading the antenna wire itself...the one that goes from the back of the pio head unit all the way to the antenna...the wire that comes with that car might suck, but i'm just reaching for sh*t....

That wire I have changed :)Damn cold here ...

Try plugging another antenna directly into the back of the Pioneer radio. Any car antenna will do. Try to rig up some sort of ground connection to the base of the antenna. The antenna mast receives one half of the radio signal. The other half is received through the antenna's ground plane. The ground plane is the portion of metal that the antenna is mounted to, usually the fender or roof. There must be NO resistance through the lead cable to either the center conductor to the antenna mast or from the antenna leads outer contact to ground. Pioneer has one of the best tuners on the market.sparky

Did that , could it be the ground of the headunit or the +12V ?? It is strange as I had same kind of problem with another Pioneer unit in the same car brand , Mitsubishi. The one from now is a Galant the old one was a Lancer and in both cars same problem with different Pioneer headunits.Damn cold here ...