founded out another problem which i think is the cause of the weird response of the VU meter. All the 10 emitter legs of the transistors are connected together which is then connected to the +Ve output terminal of the LED driver. The R, G, B output terminals from the driver are directly connected to the LED strips. But now I disconnected the +Ve supply and the R,G,B connection from the driver and instead connected a +12v terminal from a DC adapter to the transistor emitter legs and the negative terminal to the Red terminal of the strips. now it is found that all the strips are flickering continuously without any audio signal or even when the VU meter is turned off.
On further look it is found that while removing the LM3915 IC from the base there is no LED light up or flickering. So its clear that Somehow the IC is producing some noise at its output legs.. So I think this would be the problem but I don't know how to solve it.