Noise On Am Radio Problem

I installed an FM modulated XM unit in a Peterbuilt semi truck about 6 months ago. Apparently there is a new driver in the truck and he noticed that he is getting noise in his AM radio when he uses his turn signals. He is coming in tomorrow for me to see if I can fix it or not, and I thought I would see if you guys have any suggestions.

The only part of that circuit that I touched would be the antenna. Do you think it could be coming from there? The only thing I can think of doing is make sure that the outside shield of the coaxial wire for the antenna has a solid ground. I could also add a new ground to the head unit, but I didn't touch that in my install.

Does anyone else have any other suggestions? Is this a common occurance with satalite radio? I've never had anyone else complain, including my boss who and our previous installer who both have XM radio. But then I don't think he, or any of the other customers listen to AM radio.

I'm having my boss turn on AM in his system and see if it is there. I'm also doing a Sirius install today in an Escalade, so I will check it as well.

Thanks for any help.

 

I posted this on Car Sound as well, and that's what they think as well.

And yes, I did get your PM. Thank you for the help. I really do appreciate it.

 

I T-tapped to the ground at the head unit and wrapped that wire around the outside of the antenna. The vehicle is a GM, so I had to use an antenna adapter when I put the head unit in. I sandwiched my ground wire in there to make sure the ground stayed in place. Unfortunately that didn't get rid of the sound.

I did find out that some of my information was wrong. It wasn't FM modulated, but used a Sony Xplod tape deck connected to a Sony XM processor.

The sound was really wierd. It was an odd rollong, chirping sound, and it happened with the brake, turn signals, etc. I noticed that he has another beeper inside the vehicle that makes sound as well for some reason. On hindsite, I'm wondering if that is what is causing it. But I pretty much eliminated the possibility that it was caused from the stereo I think. And with all the electronics on that thing, I couldn' tell him what it was.

He asked if he could pay our shop rate per hour to hunt it down. But I personally don't know enough about semi's to tackle that. I figured it would take a week to find the problem. I would have to completely strip out the interior of the thing and start hunting. I told him to go to a diesel mechanic and see if they can find it. I figured it could be as simple as one of the many batteries having a corroded terminal creating a bad connection. But paying so much for me to go through that vehicle to find a noise that only shows up on AM radio which he doesn't liten to that often doesn't make sense.

My boss used to be a diesel mechanic, so I told him about his offer to pay us shop rate to find it. His imediate response was NO! He says that it those things are a real pain.

I am still curious. Based on the new information, does anyone know what it could be?