Sound switches from external to internal.

Hi
I have an HP Pavilion dv6t-7000 Quad edition notebook.

My notebook is acting very strange, audio-wise.

When I start up my notebook, the sound is perfectly fine and it comes out of the speakers that are connected via 3.5mm jack.

However, when I sometimes connect a USB to the notebook, the audio will switch from the external speakers to the internal speakers located inside the notebook. I have tried to reconnect the 3.5mm audio jack, but it does not fix the issue. The only way I've found to fix this problem is to restart my noteobok altogether. 

What's going on with my notebook? I have no idea what's wrong. All the drivers are updated. I'm thinking it might be a hardware issue, but I'm not too sure.