Finding a fault on a preamp board from my car power amp, what to look for?

[240sx4u]

Alright, I have a Hifonics Neptune amp in my car. I have a problem on the preamp board. The board is pretty small. About 4x3" and I have a popping and crackling from one channel. Its only when I go over bumps. Well, I pulled the back and when I push on the back of the input board I get one channel dropping out and just hum. The corner that I mess with is the one closest to the white connector near the RCA jacks.

Dumb design, but the input board is supported by the RCA jacks, my trunk is VERY high vibration from road/exhaust etc.. so it seems to be wearing on it. Amp is about 10 years old.

I tried re-flowing the solder joints for the RCA connectors to no avail. I can't see any physical distress on the board. Are there any telltale signs I should be looking for? I can take photos too. I had considered trying reflowing most of the joints to see if it helps but don't wanna cook the board or any of the IC chips (there are a few small ones).

Thanks guys - Evan

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