Sub Trouble

I just bought a boat with the sub, amps, tower speakers and all that stuff. I am wondering if anyone knows why the sub makes a continuous "thump" noise when nothing is playing in any of the settings (XM, disc changer, am/fm) I have a sub volume knob and it decreases with that, of course, but I can faintly hear the sound when a song is playing. When the stereo is on, the only non-related equipment running is the depth finder. The amps are about two feet from the sub. Kicker 12" w/ an SX6503 and a KX8504 running the tower and interior. Sounds great otherwise!
Any suggestions? Buehler?

My guess is the depth sounder is interfering with the audio inputs to the sub.

Time for a test...

Unplug the sub amp RCA's and run a temporary set from the source to the amp as far from the depth sounder cable as possible.

Or just unplug the depth finder.

Where's the pic's? I want to see the new ride....

The other easy thing you could do is unplugg the RCA's at the sub amp and see if the noise goes away. That'll tell you if it's an internal problem in the sub amp itself.

Otherwise, try what Mike or Joel said. I'd suspect that the other thing it could be is a fault with connections in the stereo.

So it is the depth sounder. I was wondering if the transducer (sp?)in the hull would cause interference.
Any idea how to get rid of it? The through hull is right in front of the engine (direct drive) while the sub is in the bow.
Hey Evan, I'll post some pics once it's out of the garage. Pretty much wedged in with about an inch to spare.

The amp is bad....sorry

I don't think so, Dave. I unplugged the depth finder and it went away.
Maybe a weak ground or something??

Yeay, check your grounds, or you may have a place where the insulation on the wires may be nicked or something along those lines. You could also try some wire that is shielded, although I'd bet on a bad ground.

Also, its possible that the transducer for the depth finder is bad. OR, maybe its because you have the boat enclosed in a garage, and the sound waves from the transducer are bouncing off the concrete floor and wreaking havoc with stuff. I would check the ground, but if its still an issue, just leave the depth finder unplugged until you can get out on the water and test it there. You might find that it works fine on the water.....just my $.02

Mine just makes faster clicking noises on land. What worked for me is shorter, rerouted higher quality RCA's, a line driver so the amp gain is minimized, and a noise filter on the 12vdc supply to the depth finder. It took all three to get rid of the noise.

Good point. It made the noise on the water but not as bad. Either way, I'll start by checking the wires. Thanks for the advice!

I've seen a similar problem with an older system on a customer's boat. Ended up that the RCAs were routed directly bellow the depth finder module and actually strap'd to the signal wire, once we re-routed that it was fine.