Hey Steve,
I checked the rubber cover on the ground and it will not work to stop the m/d signal... I think, since you seem to be doing fairly well you might just as well leave the m/d idle and just pan some material from a likely looking spot and see how you do... Try to dig down to bed rock or hard clay and pan that material...
I suspect that you are not getting a signal from the gold but from the black sand as I think you have already figured out... When you have the sensititivy set to Max. on some detectors a slight bumb or scrape, wet grass,etc. will set off the detector
Try backing off about 1/2 turn and see if the detector becomes more stable... If you can find someone in your area, a club or just a good coin shooter to buddy up with and go to a park or old house place, etc and learn to use the detector in discriminate mode as well as in all metal which is whats used for gold and relichunting... As Fla. said you have to learn to set the ground balance for the area that you detect in and this will change through the day so that you have to keep resetting the GB... Your detector might have auto ground balance so it will be automaticly balanced as you detect... :-/
I suspect that your creek is fairly rich in that you have been able to find gold everytime you went out... Once you learn to read the creek you just might be able to do pretty good, but like Fla. said maybe only able to find $15.00a day or if you can get 1 oz a day you might be able to make it pay... :-/
A good hobby but don't quit your day job just yet...

Queston----Once the creeks and rivers freeze in winter there do they stay frozen untill the spring thaw? Or do they freeze and thaw out several times during the winter? Or do they keep flowing year round?

??
Later, Jerry