Need advice: 99 Silverado radio shorting and p0430 issues

[Robzilla!]

I have a 99 SIlverado 1500 with 170k miles. The engine was rebuilt about 8k miles ago and it runs strong.

Recently, I started noticing a few issues. One is the stereo shorts out at sometimes when I hit a bump, shut the door, click the seatbelt, or when i shift (its automatic). There is an aftermarket stereo and subwoofer installed, as well as speakers (alpine stereo with jbl sub and infinity speakers). In all honesty I'm not that savvy when it comes to vehicles and I'm curious to see what others think the cause of the radio shorting out is?

Secondly is that the "Service Engine Soon" light came on. Now the truck was up for an oil change which was completed, also, that same day I put gas in. The owners manual noted that cheap gas could cause the light to come on, I used Chevron? Luckily I had a Hypertech programmer handy and noted the code that came up (p0430). This resulted in google searches revealing a "Catalyst System Efficiency Below Threshold (Bank 2)." Is this true? Also, is this referring to my Catalytic Converter or a possible faulty O2 sensor? Any feedback from someone with similar experiences will be greatly appreciated. The truck does have stock exhaust and since I live in CA with super strict emissions laws, I am considering going with an aftermarket exhaust instead of just buying a new cat system. Any comments on that would be appreciated too.

Thanks for any help, it will definitely be appreciated.

[unplugged]

Aftermarket stereo points to a fault in the installation. Pull the head unit out and check the wiring. Was an adapter plug used or was it just spliced into the harness. Either way a loose connection, or bad ground could cause your symptoms.

With the year and mileage of your vehicle I'd guess cat, but a O2 sensor is cheap enough to try that first.