Couple questions about 02 Solara

I just recently bought my g/f a 2002 Solara 4cyl and have a couple problems and hopefully someone can answer these for me

1. There's a squealing noise comming from the speakers when she accelerates.

2. When she accelerates and is playing a CD it sounds like it cuts out (gets scratchy and muffled then cuts out) but comes right back on when she gets up to cruising speed

3. Check engine light came on and i scanned it and got a code of 0420.

4. Where can I get mods and performance parts for this. The mods for my car are easy to find but i'm not sure about this one. i've seen TRD body kits and stuff which look good and not too ricerish. I'm guessing eibach makes springs for it. what about intakes and exhaust?

thanks for any help anyone posts. Its much appreciated.

for the code, it means your catalytic converter isn't doing it's job. either because your engine is burning way too much gas for one reason or another, or you have a bad cat