Hi there,
I'm getting a high pitch noise though my pre-amplifier circuit.
when I interact with the LCD menu, it changes. You can here that in the later part of the audio.
you can listen to it here
Any thoughts, solution(s) or pcb design changes anyone could suggest please?
Thank you in advance.
You can try and reduce the input impedance of that amplifier to try and minimise the noise pick-up. Try a 3K3 resistor to ground on each input.
As to PCB layout have a separate analog supply by splitting the analogue and digital ground planes and just joining them at one point. Do the same for the positive supply and heavily decouple the joine point with capacitors and join together with an inductor.
I agree with Grumpy_Mike. The analog GND and the digital GND are separated with different pins to avoid this kind of noise.
Some chips have always a little noise when the I2C bus is used.
I have seen a number of audio devices that have noise when they do something or when a button is pressed. So even commercial companies do it wrong.
Did you read the datasheet of the TDA8425 ? How many online schematics with a TDA8425 have you seen ? No one ever uses a 12V I2C bus 
The sink current should be below 3mA.
Every device on the I2C bus must pull down the current on all three parts of the I2C bus, because the mosfets will be on.
12V/10k + 5V/10k + 3.3V/10k = 2mA (well below 3mA, no problem).
Perhaps the noise will be lower with less sink current.
According to the datasheet of the TDA8425: SDA and SCL should be maximum 1.5V for a low level and minimal 3.0V for a high level. That means it is a 5V I2C bus.
Thanks. Tried from 1K to 3.6K and didn't help.
Will have to do this as a last resort as I have to do another revision of the PCB.
This I do not know, can you show me an example schematic of this and how to choose the correct value inductor also.
look at http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Specifically this image
As to the size, as big as you can afford space for on the PCB. Inductors can get physically big the bigger their value.
Just an update after long time,
Thanks to everyone's feedback, I've been reading and watching some videos. Was able understood some of things about power delivery and PCB design. With that I was able to remove the I2C noise by separating the PCB ground planes (both top and bottom) of Pre-Amp side from the rest of the digital circuitry. Made a cut on both sides, top and bottom side of the PCB.
Next revision of the board will have lot of changes.
Thanks everyone appreciate it very much.
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