Worked fine for first 3 months, then (1) speaker developed a rumble during songs with heavier bass, i think the speaker is shot, cannot seem to find Sonic Impact website for repair, any ideas? local repair person does not want to take it apart, thank you.

You seem to have opened up your speakers already. So, I think you should use your creativity to displace the parts a little so that no contact takes place even at max volume.

How new is the amp?

A single faulty solder can do that...I'd try returning in to the seller.
Have you tried a different amp with the same equipment?

Sounds like a wiring issue.

Hope I've helped
PvT

it sound like bass rumble ( or bass feedback) to me, try locating your turntable further away from the speakers if possible, and make sure it is isolated from the table or what ever it is sitting on, by some sort of rubber feet.

A common reason for 'distortion' with all bass amps can be either that the screws holding the speaker unit to the cabinet have worked loose or that there has been a build up of dust particles in the corrugations around the edge of the speaker cone, which rattle especially on the lower notes.
The solution is simple - remove the front grille and check the screws are tight. Use a vacuum cleaner to remove dust from the rim of the speaker cone.

Hello Adam Hi, it looks like your main IC amplifier inside the main bass box is bad, need to replace that IC. What are your plans, do you want to do the repair or have it service by a tech guy.

I just got that same problem too. Except its completely gone with the bass not coming back. I think it has to due with wiring because the speakers have not gone dead and there plugged directly into the outlet.

It unfortunately sounds like a blown speaker. Try getting at the speaker and gently moving the cone with your fingers. If you feel a rubbing sensation you will most likely have to consider a new speaker. Make sure you get one with the same impedance (ohms) and the same or better power handling.

Make sure the positive and negative match up between the receiver and all speakers. I had the same problem and 1 out of 5 speakers had the wires backwards.

rewire the whole system with new wires,you could have a bad ground or wire try it first if that dont work rewire

You are most likey running too much power from the amp to the speakers.. you might want to try just notching the bass down a notch or 2.. just enough that the bass will hit