Whenever I lose lock for the first time
while doing a S&G with my Promarks,
the receiver starts to buzz (a humming sound). The battery power goes down alot
faster. It doesn't seem to effect my survey, but real annoying. All my receivers do this.
I thought someone mentioned awhile ago about this buzzing sound, I forgot what was said. Again it only happens when I lose lock for the first time.
Can anybody help?

that's what's making the sound.

that's also what makes the buzzing sound when downloading :-)

It doesn't hum when downloading,
only when the "loss of lock" message
comes on. Is the back light controlled
by the power button?

The power button (red with a picture of a light bulb) serves two purposes:
When pressed and released quickly, it turns the receiver on and off.
When pressed and held for 2 seconds while the receiver is on, it turns on
the screen backlight at the low setting. If pressed and held again for 2
seconds, it sets the backlight to high. Finally, press and hold the button
again for 2 seconds to turn off the backlight.

TGhe buzzing sound is the backlight. I have observed it on when downloading also. Usually when I go to shut the receiver off after downloading the backlight will come on even though I have not held the button the 2 seconds plus.

When downloading, the light auto activates with the newest firmware version installed. The buzzing sound caught a lot of us off guard the firsy download session after installing the new firmware (several months ago .....not new as in recent, so John doesn't need to order the ProMark5 with the new L1/L2/L5 board)