Crackling sound when attaching multimedia speakers to system with 14.04 lts

My Dell Inspiron 5343 laptop with ubuntu 14.04 lts purchased in June 2015 is giving issue with audio port. When I am connecting it to any music system ( e.g my f&d a110 2.1 multimedia speakers purchased on 19th September 2015 ) I am getting a crackling sound when the charger is connected to the laptop. When I am removing the laptop charger from the laptop power connector this sound goes away and comes back as soon as the charger is connected to the laptop.( Also I faced the same issue when I connected to my friends Sony multimedia speakers system ). When I play a song or video the sound goes away but as soon as I stop it I again get this sound.

Similarly when I open the sound settings I do not get the crackling sound but when I close the settings window again I get this sound.

Kindly suggest if any one have solution for this.

Thanks in advance
Abhisek