You are hitting the protection circuit in the PRO 80's. We developed a circuit that will cut off the horn when it senses a "clipped" signal. What happens is the horn will attenuate once it senses the clipped signal and when that clipping is gone, the horn will come back on
So this is most likely what you are hearing. You are running a TON of power to the speakers. So tuning is very very important. My suggestion is to call Gyver in tech support if you get stuck. But you need to re tune for sure.
Follow the set up guide I wrote for the WS-420 off our web site. If you weren’t already. This is a good rule of thumb on setting up a system. Do not worry about where the gain is located as there is no right or wrong. Every system is different. But I can tell you that you should NEVER hit the protection circuit. I set it very high so it only kicks in when getting hard distortion. So sounds like you have the settings wrong for sure and the gains not properly matched.
Also, make sure the ipod is set to flat. If the head unit has an ipod gain input adjustment, that may need to be turned down as well.
If you get stuck, feel free to email me at firstname.lastname@example.org
and we can walk through some more things in detail.
Tuning is an art form. So don’t fret, it takes time