Highly likely that click is interference. Check to see what wires you have running next to your trim button.
Was the click in just one speaker, a pair or all?
Generally the only wires you REALLY have to worry about getting interference with are your pre-amp low level leads (RCA's). These run on A/C instead of D/C. Difference is that alternating current creates a magnetic field around it. I'd have to look it up, but how large the field is depends on voltage and amperage. Either way, in an auto application (boat, auto... same electrical), the field is generally not very large and a quality install will use twisted pairs for your low level feeds; these create a very high quality shielding effect.
Anyhow, my suspicion is interference on your low level feeds to the amp. IF by chance it's on your speaker wire (I can not tell you how unlikely this is... but anything is possible... just depends how well built the switch, pump motor and components are built)... Just replace it with shielded speaker wire (any specialty electronics store will carry it... and I'm not talking radio shack!!)
The other possibility is that your alternator doesn't put out enough amperage and the click you hear is the amp feeling the loss of power. But, I doubt your amp is drawing THAT much power... if it were, I suspect you'd be seriously over-powering your speakers (systems generally push the most power for running bass drivers; coaxial speakers usually top out in the 75-150 watts RMS range)...
Was the click in just one speaker, a pair or all?
Generally the only wires you REALLY have to worry about getting interference with are your pre-amp low level leads (RCA's). These run on A/C instead of D/C. Difference is that alternating current creates a magnetic field around it. I'd have to look it up, but how large the field is depends on voltage and amperage. Either way, in an auto application (boat, auto... same electrical), the field is generally not very large and a quality install will use twisted pairs for your low level feeds; these create a very high quality shielding effect.
Anyhow, my suspicion is interference on your low level feeds to the amp. IF by chance it's on your speaker wire (I can not tell you how unlikely this is... but anything is possible... just depends how well built the switch, pump motor and components are built)... Just replace it with shielded speaker wire (any specialty electronics store will carry it... and I'm not talking radio shack!!)
The other possibility is that your alternator doesn't put out enough amperage and the click you hear is the amp feeling the loss of power. But, I doubt your amp is drawing THAT much power... if it were, I suspect you'd be seriously over-powering your speakers (systems generally push the most power for running bass drivers; coaxial speakers usually top out in the 75-150 watts RMS range)...