Maybe someone can help with this.

My setup

Radio shack 25 watt horn
Nady 151 receiver
Nady 151 transmitter
Rio 800 mp3s player

My problem is that with the Rio I get alot of noise or hum. Ive used other mp3 players and CD players and have almost no hum. I bought the rio 800 because the other units belong to my sons and it seems everyone on Predator masters is using the Rio. Any idea what might cause this? The Rio sounds fine with headphone alone.

Spike

We had the same problem with some cordless mic's and an acoustic guitar pick-up awhile back. This was our experience.

The cheap mic's were pretty clear, the middle ones were noisy, and the expensive ones (of course) were crystal clear. After trying several, we finally found a guitar pick-up that was clear; unfortunately it cost twice as much as the cheaper ones.

The dealer that sold us the equipment said it had to do with the frequency of the electronics. Some are compatible, some are not.

He said it didn't really have to do with the price, except the more expensive stuff usually has filters to stop most of the noise.

I would try a different player first. Maybe they have changed the electronics in the Rio mp3 players since your kid's models.

Try plugging in a Walkman or a compact cassette player instead of the Rio and see if the noise goes away. It might be incompatibility with the horn also.

If you know somebody with a similar system, try switching components until the noise stops. Unfortunately, wireless stuff is like this sometimes.

There is a thread called "DIY electronic callers" on the varmint forums (page 2?). One of the posts by SDHandgunner tells of "noise problems" with the amp.

You might check it out.