The answer to 'maintenance making noise' is that there are several common causes for HVAC systems making unusual noises, including worn bearings, loose components, and issues with the blower motor or compressor. Symptoms may include grinding, squealing, or rattling sounds, and the noise may be intermittent or constant.
In many cases, these noises can be addressed through routine maintenance and repairs. However, it's important to diagnose the root cause to ensure the issue is properly resolved. DIY troubleshooting is possible for some minor problems, but it's generally best to call a professional HVAC technician, especially for complex or potentially dangerous issues.