All factory car speakers crackling... URGENT HELP!

[Ziishan]

Ok ive just installed a sub and amp on the factory head unit. I used an Alpine High To Low frequency converter, which connects to the original rear speakers wires and a ground wire and then has a rca output. Power for direct from battery, amp grounded to chassis in boot.

The amp is a MTX 350w rms, and one 12" Pioneer sub with 1000w rms. under powered i know, i have an audiobahn amp on the way to run the sub.

However with everything connected up, i tested it and the sub works fine. But ALL of my factory door speakers and two tweeters at front have crackle in them and sound fuzzy. There is no bass going to them at all, just treble, but they seem to go fuzzy.

Can anyone help in why this might be?

*URGENT BECAUSE MY CAR IS STILL TAKEN APART SO THAT I CAN TRY ANY SOLUTION ASAP*