Inductance in radio 2008 Supra

I have a 2008 Supra Sunsport 22V. We purchased this boat brand new, and this is our fourth summer riding on this boat. Every since we first purchased this boat, it has had inductance periodically in the radio. When we are riding and listening to the radio, it will randomly start squealing very loudly. It seems to happen when we are using our stereo and the battery begins to charge. This is very embarrassing when we have guests on board, and it is ear piercing. We have a tower with awesome speakers, and we would love to be able to enjoy our radio when we are out on the lake.

Usually it is signs of a bad ground, or to small of a ground.

Smithlake,

Can you provide more details about exactly what is in your boat in terms of stereo equipment, is it dual or signal battery, etc? Although you bought the boat new, there can be a significant difference between OEM and dealer installed equipment. Knowing exactly whats in the boat and what it had when it rolled out of the factory and what was installed post =-assembly, can greatly speed up the process.

It has Supra factory dual battery system. It has the original Kenwood stereo system, and it has 2 (250 & 750) kicker amps. It has four tower speakers.

IIRC, the OEM dual-battery setup uses a traditional OFF/1/BOTH/2 switch.

First thing is to confirm that ALL audio equipment shares the same battery source. To do this with a dual-battery setup, all off the stereo B+ connections need to feed from the "C" post of the switch: Both amp B+ cable, head-unit's yellow B+/MEM and any other audio gear. This insures that all the gear sees the same battery reference. This can be confirmed with a DVOM.

Make sure all the RCA cables are fully seated and have a snug fit.

Make sure the main ground cable is clean and tight.

Where is the head-unit located? If its on the helm, then I would guess that its black GND wire is terminated to an under helm BUSS. I would consider relocating it either directly to the battery or one of the amps ground lugs. Although the boat theoretically has only a single ground point, the engine, and all grounds branch off from it, there can be some advantages to having the head-unit grounded as close to the battery, like to the amps or their distribution block, or directly to the battery.

Excessive amp gain can also be a source for noise, but its typically not random, but constant.