Noise when powered by 9v battery

Looking for suggestions. The Pedalshield seems to work fine when powered by USB, but powering with 9v battery causes a very audible background frequency.

9 out of 10 times when powered on with the 9v battery, you get the background noise. But sometimes it's quiet -- it's just a question of chance. When powered by USB, you get a fairly clean signal. Is this some sort of weird grounding issue?

No está definida la ID de la APP eBay en la configuración KunenaGood idea -- I will check the test points.

It does power on and play properly even with the high pitch frequency in the background. I am using the VIN pin because the PedalShield is mounted inside of the guitar body. I have read that using the VIN pin is a bad idea and will later revise to use the barrel plug pins (for the diode protection in particular).

Tried it with a fresh, fully charged alkaline battery and with a lithium rechargeable 9v. Seems to occur either way.

The Arduino DUE is from eBay:

Is SainSmart OK?

Added a separate 5v regulator connected to the 5V pin on the DUE. The noise is completely gone. Unfortunately when powered by USB, the power backfeeds into the regulator. This is problematic at best -- very sketchy. But it's not necessary to plug into USB very often.

I'm thinking it's simply a problem with the voltage regulator in this particular DUE.

I wonder if a single 9V is enough to power the due + pedalshield without causing the switching psu to sag more deeply into it's ripples, baring it's 500khz switching freq.

I've spend most of the morning tracking down the noise issues Regular USB adapters seem to be out as well for noise. Some do ok (200-400mv peak to peak), but some (like my laptop) introduce a high pitched squeal.

Looking at the due schematic, it doesn't even try to regulate the 5v outside of a couple of ferrite beads. It doesn't have sufficient noise reduction caps on the board as well.

The best I've been able to do so far is 6AA batteries (which gives me 100-200mv peak to peak when writing zeros to the DACs). I'll try putting together a 7805 circuit and going straight to the 5v in pins - looks safe enough on the schematic (as long as I don't reverse the pins ), that's basically what the higher voltage switcher is doing from the USB's point of view.

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