Rumble, Pop, Bang: Why Is the Furnace In My El Dorado Hills Home So Loud?

Why is the furnace in my home so loud El Dorado HillsEl Dorado Hills isn’t at risk of freezing over anytime soon, even though, technically, it is autumn around here—it’ll probably be weeks before we really start to rev up our furnaces. But, we’ve had a couple of chillier nights lately, and some cold Sunday mornings that the local vendors at the El Dorado Hills Town Center Certified Farmers’ Market have certainly been awake for. If you’ve already run your furnace this fall, even for a few hours, you may have thought the fans sounded noisier than you remember. And, you might be right.

Don’t chalk it up to your imagination—it’s important to know that a loud or unusual sound from a furnace can be a major predictor of problems throughout your entire system, from the ducts to motor, or even the burner. If so, you may be in for some trouble this winter unless you let a local HVAC professional diagnose those scrapes, pops, and bangs. Here are four furnace noises I start to get calls for this time of year, and a little insight into just what may be behind them.

Noise #1 – A Metallic Scraping Sound

You Hear: A loud, metallic scraping sound. You will likely know this sound right away. It’s a lot like nails on a chalkboard, except it’s metal scratching against metal.

The Cause: If you hear this sound, the blower wheel might have gotten loose from the motor shaft, and now it’s hitting the housing as it rotates. Or, the blower wheel might have broken altogether and need to be replaced. A third, but less likely, cause is that the motor mount broke, and is no longer holding up the motor and blower.

It’s actually a good thing this sound is so annoying because if you don’t shut your furnace down upon hearing it, a loose or broken blower wheel can cause extensive damage to your unit as it pummels the housing. Don’t run your furnace if you hear this sound. Shut the system down and call your trusted, local HVAC repairman.

Noise #2 – A Pop or a Bang

You Hear: A pop or a bang when your furnace starts up, and then another pop or bang when it shuts down.

The Cause: If your furnace gives you a start every time it starts, your home likely has an HVAC system that includes ductwork made of sheet metal. The loud pop or bang you hear is caused by the return trunk. When the fan gets going, the duct makes a large pop-in noise because it’s responding to the negative pressure from the fan. Then, when you turn the furnace off, a pop-out noise happens because the pressure has been released from the duct. The most common causes for this are undersized or flimsy ducts, closed vents, or a clogged filter. Sometimes, this means your HVAC system requires additional bracing.

Noise #3 – Thumping or Vibrating

You Hear: A thump or a vibration, kind of like a broken washer when it gets out of balance or crooked.

The Cause: Your blower wheel is probably unbalanced. Sometimes, even the motor can get off track and start humming. Although not a critical problem in the short-run, if left unchecked, out-of-balance motors and wheels can create bigger problems within your HVAC system.

But, if the furnace isn’t working at all, and you still hear this loud vibration or hum, you probably have a bad indoor fan or capacitor. The capacitor is the part of your furnace that provides it with electricity, and it almost always needs to be fixed by a professional with a multimeter or a similar tool.

Noise #4 – A Rumbling or a Shake

You Hear: A deep rumbling or a violent shake coming directly from your oil or gas-fired furnace.

The Cause: If you hear this sound, turn your furnace off and call for HVAC service immediately. A rumble inside a gas or oil-fired furnace is due to a serious issue with the burner.

There are right times and wrong times to attempt DIY HVAC repair. This is, without question, one of the wrong times. Don’t put yourself in danger—a bad burner can lead to hazardous gas being emitted, a fire, or even an explosion. If you hear a rumble, do not use your unit and call your local HVAC professionals immediately.

Lend your ear to your furnace this fall when the temperatures drop, and the noises in your HVAC system start to speak up. The reasons behind those furnace noises are varied, but some of them could mean real trouble. Make sure you know what exactly it is that your furnace is trying to tell you now, or you could be left out in the cold this winter.

If you’re hearing unusual noises from your furnace, get in touch with Bell Brothers, your local HVAC experts, before the weather really cools down for the season.