[SmOgER]

When I bought it everything was perfect. It lasted for a couple of weeks and now all of the sudden I'am starting to hear those radio sounds like when you put your phone to close to the speakers... Nothing has changed, same cable, same smartphone, I'am even wearing the same clothes (lol). 
Why the ... is this happening? It's annoying as sh!t... 

 
Yes, it is close to the phone, but the same day after buying it I couldn't reproduce any interferences no matter how hard I tried and it was like that for a good couple of weeks. 
 
PS. FiiO E6

 

[NA Blur]

The E6 like many other portable headphone amps is susceptible to EMI ( electromagnetic interference ).  I get the problem you describe with my Bithead when I place it too close to my iPod touch.  I think it is the EMI from the iPod touch latching onto the Bitheads signal path.  Try keeping your phone and E6 farther apart.  It probably depends on battery life, proximity, and cable path be it straight or looped.

 

[SmOgER]

The strange thing is, it only happens with left channel....
Is it possible that somehow radio shielding got damaged?

 

[SmOgER]

How do you disassembly it? it should came apart with a knife/screw driver, right?

 

[SmOgER]

Bought longer extension cale. Same result. Big interference when mobile data or call is active... 
 
Any ideas?

 

[NA Blur]

When the issues arise how far apart is the E6 from the phone?

 

[SmOgER]

it makes no difference if it's a 0.1 or 0.5m. 

 

[NA Blur]

Perhaps it is the battery being lower than normal.  Give it as well as your phone a nice charge and see if that is the issue.  It sounds like EMI, but it could be a noisy battery ( capacitance issue ).