Found out where white noise was coming from

So my Retrosound Zuma radio has always had a constant white noise.  At first I thought it was the Rockford amp I have running the rear speakers and sub, but then I discovered it was in the front speakers too.  Those are run solely by the head unit.  After playing with ground loop isolators on the inputs as well as completely disconnecting the inputs, I tried an antenna filter.  That didn't do anything either.  So then I was convinced it was a bad ground.  So I cleaned all grounds and even added a couple body to frame connections.  Still white noise...

At that point I was frustrated...  all the wiring in the car is new, all the speaker wire is new, and even all the speakers are new.  I contacted Retrosound, and they agreed something wasn't right.  While in contact with then I added a power filter to the 12v line to the radio.  After adding that I discovered something about the noise.  It only happens when the EQ in the radio is used.  A preset or using the bass/treble adjustment.  Any amount of EQ (positive or negative) and the noise started.  It was a constant level of noise unless volume was set to 0.

After telling this to Retrosound they said I would need to RMA it so they could test it.  However since its over 1 year old (the warranty length) I would have to pay full price for the new model to replace it if it was bad.  Drives me crazy to hear things like that...  It's always been this way, and I didn't have the time until now to prove it was a problem with the radio.  Why would I bother sending it in?  It's clearly the radio...  Seems like the least they could do is offer a discount on the new model.  I mean this radio has maybe 2 hours of total use on it and has been in the car for about 1600-1700 miles.

Still deciding if having an EQ is worth the cost of the new radio.