Find better grounds for h/u and amp it will solve your feedback issue, I highly doubt it would be a bad rca ground in the amp itself, lights dimming are you sure the sub/subs are wired correctly? Get ahold of a volt meter and check voltage drop at amp as everyone else has suggested, we can't quite help if you don't do things that are suggested for more help, replacing batt up front will do lots of good things if it is a few years old, also set your gains with a dmm you should NOT need bass boost at all How to properly set your amplifier gains using a DMM Step 1: Determine the RMS output of one channel of your amplifier and the rated RMS input of your speakers/subwoofers you will be using on that channel. Select the lower of the two for using this chart http://db.tt/ZiZA5Yyq Step 2: Match the impedance (ohms) you have on one channel of your amplifier to the column on the chart. Step 3: Turn your amplifier gain all the way down. Step 4: Disconnect all speakers/subwoofers from the amplifier Step 5: Insert the leads of the multimeter in to the channel you are setting (if bridging an amplifier use the terminals you would be using) Step 6: Set the multimeter to ac volts Step 7: Turn on the head unit, zero out all EQ settings, turn off all filters (low pass/high pass), and make sure loudness is off. Step 8: Play a 50hz or 60hz test tone Step 9: Set the volume to 75%-80% of the maximum volume on your head unit. Step 10: Start playing the appropriate test tone for subwoofers, 1000hz for mids/highs Step 11: Slowly turn the gain until you obtain the voltage from the chart Step 12: Turn off the head unit, unhook the multimeter, hook up your speakers/subwoofers Step 13: Adjust EQ to desired settings without distortion/clipping its that simple