Gurgling Noise from Sink
It is nothing to be worried about, the vent that prevents the tub and toilet gurgling  is probably down stream from the sink. When the sink drains it blocks the vent and creates the vacuum that sucks air from the sink trap (the glug glug you hear)  there are ways to reduce or possibly eliminate the noise by adding an air admittance valve under the sink counter but these can cause problems if not properly installed or if they get gunk in them. 
So if you want to eliminate the noise look up air admittance valve (there are some answers here that even have photos) 
The noise won’t hurt anything and doesn’t have anything to do with the pipe in the ground , just the vent, if you allow the sink to drain slowly it won’t make the noise in most cases.