Strange sink drain issue

 A few weeks ago our bathroom sink drain started gurgling.  It happens
about 30-90 seconds after you stop running the water at the sink.  It
wasn't happening previously and the house was built in the mid 1960s.
The gurgling also seems to be only caused by running water at that sink,
flushing the toilet or running the shower doesn't seem to cause it.

Unless a flying squirrel jumped down the roof pipe, I don't think
anything has happened to the plumbing vent.  Also, the sink has been
draining ok, but maybe not as quickly as it used to.  We have copper
drain pipes and I'm not sure if drain openers like Drano (NaOH) will
corrode the copper.

Any ideas?  Thanks!

 

Plug the overflow drain (wet your hand and press against it) then run
some water and use a plunger. I bet you get a whole buch of evil
smelling crud coming up the drain into the sink...

Hair, soap scum etc. Skundge buildup.

If the sink has one of the built-in lever driven plugs, disassemble and
remove it. Betcha it's filthy.

Use a drain cleaner, plunge, drain cleaner, plunge. If you still have
the problem, disassemble and clean/replace the trap and/or the sink.

djb

--
Life. Nature's way of keeping meat fresh. -- Dr. Who