Why is my toilet making a gurgling noise?

[Amanda]

My toilet's started making strange gurgling noises after the sewer lines on my street were cleaned.

Is this normal?

[home improvement guy]

In a word, no. It's unlikely the sewer line cleaning caused the problem.

It's possible that the cleaning disturbed and worsened an existing blockage in your sewer lateral, but even that would have involved a problem already underway.

No matter the cause, though, don't ignore a gurgling toilet. The weird noise occurs when air escapes backward up through the toilet, and means you've got a blockage somewhere, probably in your sewer line, toilet or vent stack.

Your sewer line is the most likely culprit.

Numerous things can block it, including tree roots, debris or odd items flushed down the toilet. A sewer cleaning company can clear the line with a standard cleaning, which should cost between $250 and $500.

If it's the toilet that's blocked, the plumber will probably need to pull it, remove whatever's stuck and replace the toilet. That job could cost a few hundred dollars.

Plumbers have found everything from Popsicle sticks to cell phones to rubber duckies blocking toilets, so the lesson here is not to flush anything except body waste and toilet paper. Plumbing pros say even so-called "flushable" wipes can create a clog.

If the blockage isn't in your main sewer line or the toilet, it's almost certainly in the vent stack, a pipe that rises from your plumbing system and out through your roof. The vent stack - a crucial part of a plumbing system - prevents sewer gas from backing up into your home and helps water flow smoothly. A blocked vent can lead to big problems.

Think of the vent as a straw stuck in a glass of water. If the straw is unobstructed, water flows freely through it. But if you put your thumb over the top of the straw and remove it from the water, the water stays in the straw. A vent blockage is like your thumb on the straw, and the gurgling is caused by air trying to escape another way.

Debris, often from an animal nest, is the most likely cause of a blocked vent is debris. In some cases, stacks can become damaged. In winter, they may freeze over.

The cost of clearing the vent will vary quite a bit, depending on what's actually causing the problem, but expect to pay $300 or more, since the work will probably involve someone getting on your roof and manually clearing the blockage.

Now that you know the possible causes of your gurgling toilet, the next step is to hire a plumber who has a good online reputation and is appropriately licensed, insured and bonded.

Here's hoping your cacophonous commode will soon be silenced!