New head unit, feedback in right door speaker

Hi,

Just purchased a Sony MEX-BT2900 head unit (http://pdf.crse.com/manuals/4197991111.pdf)

Installed in the car (2000 reg p38), with the below wires in the back of the factory head unit:



I installed originally on Monday, plugging the grey and brown plugs into the Sony loom adaptor. It all worked fine.

I received the PC2-36-AMP2 from Nexxia yesterday, which is what I believed I needed to plug into the amp.

I plugged this in, and when I turned the radio on, I got awful feedback from the right door panel upper speaker.

Unplugged and went back to Monday's set up, and got the same feedback.

I probably need to follow wires through to that speaker, and also need to remove the horrible aftermarket samsung car kit that's been installed, but thought it was worth asking for any other suggestions from anyone who's experienced similar!

Thanks


P.S. Before I took the original head unit out I turned volume to loud, as per Nexxia instructions.

There was a member on here who knew the P38 Audio system really well - Clarkie or Clark120 or something like that...search for his posts he describes the fitting of aftermarket system and what adaptors are needed etc....