My room light and boot light is dancing / blinking to the tune....

What could be the caused?

I have no amps, just changed 4 speakers (2 4" Sony Xplod dashboard speakers + 2 coaxial 6" x 9" speakers from Carerlet - a brand with a Scorpion picture) about 3 months ago) and i have a single disc Pioneer player. I hate it because it's makes my car like a clubbing area.

how old is your battery?

Old? Maybe 1 year + i guess.

How loud had you been listening? And how old is your car?

Sounded like a weakened grounding issue.

Not very loud, i put at 15 volume for CDs and tuner.

Car already 7 years old. But it beats to the song more when playing CD.

Sounds like either dying battery or grounding issue. Google on "the big 3 upgrade", you could add an additional single 8-gauge or 4-gauge from your battery's negative terminal to the car body to see if it helps with the issue, as the older your car, the stock thin grounding wires starts to oxidise and lose efficiency.