My background is Industrial, Commercial, & Residential combustion & appliances. I often also consult to Commercial & 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 & turbulence (low pressure drops). This results in quiet & efficient flow.
Many plumbers enjoy the speed & 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.
Ok, just got off the phone with a guy from our regional building department. The conductor that is buried with the gas line is NOT meant to electrically connect the metal pipe in the garage with the main service line (& therefore house, which has metal pipe from meter). The conductor is a tracer and is only there to assist in locating the gas line. It should not be connected to the pipe at either end.
So with a plastic pipe on the gas, there is no alternate conductive path back to the house, so I'm good on Requirement 2. I just bond the neutral & ground at the sub-panel and put in two grounding rods (which should have been there for the old system as well).
Best Answer
UPDATE: @doozit commented below that this document was just a proposal, which wasn't accepted. (It isn't described as such on the ESA webpage)
A quick google search found what looks like the answer in the Ontario amendments to the Canadian electrical code on the Electrical Safety Authority's page
This reference might be enough for you and your electricians to break the tie:
So it looks like you don't need the receptacle as long as a cooktop or oven is installed.