When your central heater turns on, you should hear a hum, but you shouldn't have to raise your voice to speak to someone right next to you. An excessively noisy heater is a sign that you may need to get the unit repaired. However, you should check a few simple items first because sometimes these simple items create a racket. It is possible that the problems your heater is having with noise are due to multiple issues, but that makes taking care of the smaller stuff even more important because that will make it easier to fix the larger issues.
Check the Vent Closures
If the noise you hear involves a lot of whistling sounds, chances are you've got a vent somewhere that is closed. The force of the air traveling through the slats of the vent creates a whistling sound, much as trying to blow air through pursed lips creates a whistling sound. The whistling can happen when the vent is mostly closed but still open a bit, so don't assume that vents that are partially closed are not contributing to the sound. The easiest thing to do is to open all the vents you have fully, and then if you still hear the sound, search for vents that might have been hidden in storage rooms and other out-of-the-way places.
Check the Filter
The filter is a simple part of the HVAC system that seems to be responsible for so many heater and air conditioner problems. Basically, when the filter becomes so clogged with dust that air can't travel freely through it into the intake ducts, it can increase the noise level throughout the system as the heater struggles to pull in fresh air. To fix it, change all filters — not just the one at the furnace but the ones in the intake vents for the air conditioner, too. You need to cover all bases here.
Once those two issues are checked, you have to consider more complicated issues. For example, the vents and ducts themselves could be to blame. You could have air leaks that need to be patched or something loose could be causing additional noise. It's also possible that the blower itself is starting to break down. However, now that you know items like the filters aren't to blame, it could be a lot easier to track down the real cause once you have a heating repair company like Hospitality Heating and Air Conditioning Inc take a look at the system.