Adding an amp would make them sound better and play louder, but they should play at a reasonable volume and sound clean directly from the head unit. The symptoms you describe would inicate an intermittant wiring problem, either a pinched wire, or strands of wire touching on the terminal strip at the crossover. If you add an amp with wiring problems to the speakers you can damage it.

Ok, I'll go into a little more detail on how I wired these. On the drivers side I used the stock red wire as positive and the other wire as negative - does this make a difference? On the passenger side I tried both wires as positive and couldn't really hear a difference. Which is supposed to be positive? Next I wired positive from crossover to the red terminal on the mid speaker and negative to black. Finally, if I remember right, I used the wire with the black stripe as negative for the tweeter and without stripe for positive. If this is incorrect Please tell me.

On the crossover, I placed the bare ends of the wires into the holes and then tightened the screws. I am thinking about undoing this and putting the wires directly under the screw heads on the top of the crossover plate. Would this make better contact? I don't think there could be any crimped wires etc. as the speakers worked fine with the stock speakers. I should probably just dump the whole lot and start over!

Ok, thats long enough. Thanks.

The more power that you send to the speaker will allow it to hit the ranges that the audio track is requesting to it better and more precise. You are hearing scratchy sounds because it is unable to move the cones as fast and as far as it needs to. In plain speak.

Are they duel voice coiled if you hooked up the jumper wires wrong they would only play a certain amount of sound . if they are look in the instructions for how the jumpers should be hooked up.