head unit or hd radio box clipping?

Hello and thanks for taking the time to assist me. I have searched the forums and can not find any threads/posts/topics similar to my situation.   
I have a 99 gmc safari, awd. I put in my, working fine on the harley, deh-p600ub head unit with pioneer external hd radio kit. wired it all in and everything works fine, but here is the part that confuses me... when on the hd radio ONLY and driving, does the stereo or hd radio unit clip out at about 2/3 to3/4 max volume and i have to cycle through the inputs or turn unit off/on to get hd working again, at a lower volume too. When sitting in car, and no engine running this doesnt do this. it also doesnt do it on cd, usb input when running! only on the fm hd radio input while driving. now, lets add this in since I think its related. My Escort 8500 radar detector, works fine in my other cars but in this one, when accelerating ONLY, does it set off the laser alert. I researched this on some RD forums and they say its engine noise issue from coil, distributor or ground loop issue most likely. I replaced the distributor cap and rotor, no change in symptoms. Plug wires look ok, all are snapped in ok. Before I go and change wires and coil, am I barking up the right tree? I am not sure if the HD radio is resetting after it clips out but it does take a few seconds before it works once I immediately cycle through the inputs back to that input. My hunch is the issue comes from the FM antenna to the HD radio, being amplified(?) then when in the head unit amplified again and causing the disturbance. So, do I have an engine noise issue or groud loop fault? Either way, I am not sure how to approach eliminating either one and troubleshooting both. One time when I first put the head unit in, i heard the noise in the speakers but it DID NOT go in sync with engine rpm's. That makes me think more of a ground issue. But I am anxiously awaiting some input and learning how to troubleshoot this. Things I did when connecting stereo, I did wrap electrical tape around every solder connection and the fm antenna adaptor, from gm to standard. I did not do anything to the rca plugs hanging off the back of the head unit. the hd radio and head unit are connected via pioneer bus cable. Thanks again for any ideas!

As far as the "noise" issue goes, if you have noise when the key is on but the engine is not running then it is more likely to be a ground loop issue and in any event changing the ground straight to the chassis would be a good idea. IF you have a whine when the engine runs and the volume is turned down and it whines when revving the engine AND you have already taken the ground straight to the chassis then it could be anything from spark plug cables to a fault in a diode in the alternator. Also check the ground cable from the battery to the chassis has a good clean non corroded connection. There are always isolators that you can use on the power ground and ignition wires to the radio but they are just a patch NOT a fix for the problem. NOW, for the hd volume cutting out, that could be the antenna adapter or make SURE the power lead to the amplified antenna is getting power. If so then it could be a faulty antenna or even the hd tuner in the radio its self. Good luck.

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Gary Sather

Gary, thanks for replying. I do not 'hear' noise anymore, with or without the engine running, that was only the one time when I installed the unit initially. I had to take it out to add the HD radio box and install the rear connecting usb and aux ports.I do not have an amplified antenna.   I was referring to the signal coming from the hd box to the head unit being amplified by the hd convertor. Maybe its not amplified, but it is demodulated and converted to a signal the head unit processes, thus I was thinking that box is either deprived of power when the head unit is running, they both are powered over the same power and ground. I will change the hd box to power from the cig outlet, run a fresh ground to the frame and see what that does. I will put electrical tape over the ends of the rca connectors not in use.
Like I said, the fact this ONLY does this when on the HD radio tells me that the issue does involve the HD box. Like i said, there is something happening when running and accelerating as my Laser goes off when I do that, EVERYTIME.   I will try to do this today or tomorrow and post my results!