I had same/similar issue with U310BT when I had it.

http://avic411.com/forum/viewtopic.php?f=53&t=30467

Basically, it has static noise after each button press (hard & soft keys). It's hard to hear or notice when driving & playing music. However it's very noticeable when the engine is off.

Any suggestion?

Only thing I didn't follow the installation guide is the grounding the hand-brake wire (hardwire by-pass).

What kind of a car is it? It sounds like it could be the amplifier for the factory sound system causing the extra noise. i am not an installer so i do not know the solution for it but this is something i have come across every now and then.

It seems it got better now. I don't notice it much.

btw, I do not have factory amp.

I get this on my 900BT. It spurts it on whenever any audio is output but stops when the source is changed or something like that. Its kinda like an old LP hiss but without the crackling. I wouldnt mind if it was soft but its pretty loud even on about half volume. I discovered that making the eq flat makes a lot of it go away but music sounds so much better with a bit more highs and bass

I have this happen as well...on the ipod. Its almost like you can hear data being transfered from the pod to the unit. Annoying but it does it one mine as well my friend...no worries its your deck.

Another thing I noticed with x710 is that audio source volume is different depends on the source (CD, MP3 (USB and SD), FM, and AM). CD is the loudest, so I adjusted with HLA(?).

Also, the system sound volume differs MP3 (USB/SD) vs CD/FM/AM. I think it's due to WinCE handling the multiple WAV/MP3 playback (system sound & MP3).

Oh well... overall it works great. I'm pretty happy with it.