Weird Problem with Car Audio or Wiring ?

I have installed JBL Components , pioneer woofer , alpine amp in my VW polo . k, the problem which i am facing is , sometimes when i start my engine and play system , only Woofer works then i have to put vol to max and min , try to rotate volume buttom quickly up and down , then sound comes in components. This is happening from last 2 months. I thought it is wiring prob, so i checked whole wiring 3 times but still prob arising.

Sometimes sound come from one side component only .
Wat could be the real problem ?

its a 4 channel Alpine orig amp . First the single wire (JBL KIT ) coming from HU is bridged with component. Then few days back . i installed separate wire for woofer & components. Now there is two diff wires connected - 1 for woofer n 1 for components. First i installed amp under front seat then i thuoght it may be wiring prob if some1 sit in back seat so i moved amp in boot but still same prob .

I was using same amp & woofer in my Dzire from last 3 years .it was working fine with no prob. Componenets & HU i bought new .

Hard to diagnose without actually looking, but from your description it looks likes you have inadvertantly cross-wired two speakers instead of them being independent of each other - perhaps a mistake while bridging.