Porsche 996 1999 Stereo Help

[AndyT955]

I have a 1999 Carrera 4 with a 6 speaker system Haes Amplifier, I have started to get muffled sound from the front door speakers (like a blown speaker) have changed the speakers but no better.Could it be the amplifier ?

Anybody got any ideas ? or know anyone stereo specialists in the kent area who could have a look at it ?

Thanks