When a car burbles, it's usually an indication that the engine is running too lean. This can happen for a number of reasons, but the most common cause is a faulty oxygen sensor. The oxygen sensor is responsible for monitoring the amount of oxygen in the exhaust gases and adjusting the fuel mixture accordingly. If it's not working properly, the engine will run leaner than normal and may start to misfire. In some cases, you may also notice a decrease in fuel economy.
If your car starts burbling, it's important to have it checked out by a mechanic as soon as possible. Running lean can cause serious damage to your engine over time, so it's best to nip the problem in the bud before it gets any worse.