Vixia R40 audio input issue

[Drumin]

I picked up this R40 camcorder and found out that in order to use an external mic I have to use a powered mic. A friend loaned me his Audio Technica mic and a portable 9v preamp. It almost works great... The problem is that when there is no noise, like when it's sitting idle for a few seconds, the audio level increases as if it's trying to pick up quiet sounds. As soon as I start talking that noise drops out but, the first words out of my mouth are flooded by this "white noise" before the level goes normal and my voice is clear with no hiss. If I don't talk for a couple of seconds the noise floor slowly increases until I start talking again. We tested the mic and preamp on a Kodak Zi8 and it works flawlessly. Help?

TIA

[IamintheUK]

That's the automatic gain control working. You will have to look at the R40 manual to see if it has a manual level control mode.