Take a can of air to that amp, that's a lot of dust on it= bad for electronics, that bolt would cost no more then $2 from a dealer. Seems like the last owner had messed with the jeep, I'd look deeper into the jeep and see what else has been messed with.
2001 WJ 60th anniversary edition 4.7 quadra-drive
5" hybrid lift, 265/70/17 Guard Dogs load E, bilsteins 5100's, addco sway bars, JKS front quick disco's, JKS adjustable track bar, KOR durometer track bar bushings, IRO crucial path front L.A.s, 1.25" Spidertrax spacers
Colorado Jeep Club Member #262