Active Preamp From Guitarfetish

[vicarious484]

Hey, I bought a preamp from Guitar Fetish with 3 Band EQ plus gain on a trimpot. They say just stick it in the cavity with some double sided foam tape. But when I turn up the gain, I almost hear this shooshing sound like rain or a train that repeats every couple of seconds. Is this a natural byproduct of gain that can't be avoided or the poor design in Guitar Fetish preamps?

Here's a link to it:

http://store.guitarfetish.com/guprgaourbeu.html

I noticed other manufacturers like Reflex dip them in wax and put them in a plastic case. Would that help if I potted mine as far as noise reduction goes? Obviously, the trim pot couldn't be used unless I drilled a hole in the case. Does anyone have any recommendations for doing this? I actually bought some Reflex pickups but it didn't have a preamp box with it so that's why I'm using the one from Guitar Fetish.

Thanks for your input!