First off, brief introduction: I'm a Computer Engineering student currently taking time off of school, working on a boat, started working with the boat's electrical systems because hey, I understand DC power! Now the issue: I wired in a PA system to our VHF radio unit. It works great, except the system was designed to be 2-way. When you hook the system up to a bullhorn, it works as a microphone and can transmit back to the VHF unit. We had a bullhorn, but it got corroded and we replaced it. Now we have waterproof speakers that are fine except they pick up FM radio and send that back to the VHF unit. You don't hear the FM radio over the speakers, just back at the VHF unit, and transmission from the VHF to the speakers seems to be fine. This isn't a problem, per se, but it's annoying to hear. The problem is with the speakers, and I tried putting a ferrite ring on, to no avail, although a different one with a different stopband could work. What I'm unsure about, is technically the system is working the way it should, we just hooked up something other than what the system is designed for! I do know what frequency radio it's picking up (100.3 MHz) but I don't know what frequency it outputs when the PA is in use. Keep in mind I only have access to a multimeter onboard. Any suggestions?