Audio problems on Hammerhead Rev D 2007

[HeatSink]

Hi everyone,
I recently finished my Hammerhead Rev D PCB, but I encounter a very annoying problem. My Hammerhead has a very high audio-frequency when no target is detected. Since I am new to the world of metal-detectors I don't know if it this is normal or not. I followed the instructions on Carl's article thoroughly and it seems to work so far, except the audio problem. With the DIY-coil from the article I am able to detect a ring about 8 inches above the coil. In this case the audio drops in frequency and slowly retunes itself back to the high no-target frequency (VCO-audio & Autotrack on). The only thing I noticed is that the threshold-pot doesn't seem to affect the output very much ...
Test setup:

- The circuitry is powered by a bench PSU

- The pigtails of the coil are directly connected to the PCB (the coil lies next to the PCB)

- I am currently inside the house (due to the test-setup it is difficult to take everything away from mains or other parasitic sources), but does that affect the sound that much?

I can't think of metal-detecting whilst listening to this very high pitched sound, even with the volume turned down.

Hope anyone can help me.

[Silver Dollar]

My guess is you used part of the nonVCO and VCO options. I was redrawing the schematic and had to ask
how to wire Q5 as that's where VCO and NonVCO part ways. The threshold not working may be a clue too.
The way it works is a target signal creates a current into the 555 (IC9) through IC8 which sets the threshold.
I thought you set it for a low speed cluck with no target and the frequency increases when a target is present.
Make sure you didn't install Q10...

[HeatSink]

Thank you for answering! Yes I did have installed Q10. After removing it, the whole thing now responds more to the pot settings. The output now varies from a dead silence to some sort of white noise. But when I approach the coil with a piece of metal the audio frequency drops an finally mutes when the piece is very close. Beforehand I didn't pay attention to the jumper settings around IC9. How schould they be set in this case?