PhatNoise uh, - system noise

[arexsvn]

I just flashed a Kenwood Keg to Mazda PhatSys and got it working well in a 2004 RX-8. I now notice quite a bit of system-sounding noises at (radio) startup and between tracks. It seems to come an go depending on hard drive activity in the DMS. I don't recall any sounds like this when connected to the Kenwood head unit in the original config. Do others hear high-pitched whines or buzzing? It sound just like the PC kinda noises that would come from an over-amplified set of PC speakers when connected to a computer. The noise goes away when I hit MUTE. Perhaps a grounding issue? I am using the stock Mazda cable from the dealer.

[timps]

With my Audi box I could hear the hard drive between tracks and on start up when connected to the Audi headunit. I change the headunit to a Kenwood and re-flashed the box the noise stopped.

My view at the time was either a cable or grounding issue fortunately for me the change of headunit solved the problem so I did not pursue it any further.

[S80_UK]

Yes - typically this is a cable or grounding issue - that is that the ground connection at the head unit and the ground at the Phatbox are not exactly the same, either due to electrical noise from the Phatbox, or from elsewhere in the vehicle (such as the alternator).  The result is that this ground difference appears as a part of the signal on top of the audio.

Sometimes this can be cured by making sure that the Phatbox connects to ground only at or near the head unit (sometimes through the interface cable).  But getting rid of one source of noise in this way can make another source more noticable.  When I tried this I had alternator noise which I could get rid of, but I then got the digital system noise from the Phatbox instead.  

Often some experimentation is needed, including possibly isolating the Phatbox casing from the mountings (if not already isolated) or actually grounding the casing if it was isolated.  But I recommend that you check for any significant voltage before adding wires.  You should only be able to measure tiny fractions of a volt if there is a difference.

As a last resort (but often a very effective one) you can put a ground loop isolator in the audio path from the Phatbox to the head unit.  I did this when putting a VW box in my Volvo (see my wiki page for a bit more on  this - http://wiki.phathack.com/VW_Phatbox_to_Volvo_Transplant_%28How_To%29 - about half way down).  This was cheap and completely successful in my case.

Les.

[arexsvn]

Thanks to all who replied. I appreciate the help.

I switched to a VW/Audi PhatBox that I grabbed to replace the Kenwood Keg. It worked fine flashed as a Kenwood replacement. I flashed the firmware to Mazda and installed it there. Now, no more noise in the RX-8.

Maybe there is a finer balance than I realized between how Kenwood matches things and how Phatnoise does them.

Summary:
Kenwood Radio + Kenwood Keg = no noise
Kenwood Radio + VW Phatbox = no noise
Mazda Radio + Kenwood Keg = NOISE
Mazda Radio + VW Phatbox = no noise. Sweet!

[S80_UK]

Some variants of the Phatbox have different arrangements for the handling of the system and audio grounds.  It would not suprise me if headunits also had variations as well as there cabling schemes.  So, well done on finding a combination that is successful!