Gas stove whines/hums - is this a safety concern?
My background is Industrial, Commercial, &amp; Residential combustion &amp; appliances.  I often also consult to Commercial &amp; Residential Cooking Equipment OEMs.

The noise you are most likely hearing is a high-pitched hum, caused by turbulent flow in some pipe fitting.  Most frequently, the source is an undersized or too lengthy flexible pipe fitting.  If you notice, black iron pipes have straight smooth sides.  This does not guarantee laminar flow, but it does greatly reduce internal friction &amp; turbulence (low pressure drops).  This results in quiet &amp; efficient flow.

Many plumbers enjoy the speed &amp; efficiency of flexible tubing to make the final 18" or so easier to pipe to the appliance.  Flex hoses are flexible by using overlapping corrugated sections.  They cause VERY turbulent flow...but are acceptable under certain conditions...and very quiet when sized and used properly.  There are very specific flow rates assigned to each individual flex line manufacturer's rating.  Exceeding those rates will always cause excessive pressure drop (lower firing rates to you) and usually an improper air-fuel ratio (although not necessarily in atmospheric-type burners)...but they will ALWAYS cause a whine or loud hum.  

Increase the flex line size (less than $30 in parts), or try to decrease the length...substituting pipe.

Warning, a burst regulator diaphragm can cause a noise, but the gas odor (caused by the chemical mercaptin) will be evident as it leaks through the regulator vent.  Accumulations (natural gas floats in air) are explosive.  You would easily smell the gas.  LP gases have a 1.5sg (Air is 1 specific gravity) and will drop quickly in air...and also go down drains!  A gas company can easily check for leakage (and should)...however, their meters check in parts per million (ppm).  Gas is only combustible in very defined %.  A room at 100% gas will not support combustion...but do not open the door and introduce oxygen!  Accumulations build to %...and the danger...and exceed the flammibility limit and self-extinguish (not enough oxygen).  Competent gas appliance installers use a method of a soapy water spray (or a specific leak detection soap) brushed onto every joint.  They just look for the bubbles.  It is very accurate to show problems (many OEMs use this approved method to detect leaks).  Any joint can leak in ppm (some pipe dope will outgass and set detectors off), AND be safe AND in full compliance with all standards.  No fitting is leak-tight.

Bottom line, change the flex.  If it is not a code issue in your area...it is a 15-20 minute job by a normal plumber.  Best Wishes.