A property manager in Royal Oak spent three weeks treating a tenant’s noise complaint as a customer service problem. The tenant, a five-person law office on the fourth floor, said their conference room hummed every time they got on a call. Nobody mentioned HVAC. Nobody mentioned the rooftop unit sitting almost directly above that room. By the time a technician actually walked the roof, the mechanical cause had been there the entire three weeks, and it had nothing to do with how sensitive the tenant was being.

Why Noise Is an HVAC Problem Wearing a Different Complaint

Rooftop units, chillers, cooling towers, and boiler rooms all generate mechanical noise and vibration as a normal part of operation. Buildings are designed around that fact. Acoustic separation just means enough distance and insulation between equipment and occupied space to keep noise below a tolerable threshold. ASHRAE’s own design guidelines put a number on that threshold: private offices and conference rooms are designed to run at NC/RC 30, roughly 35 dBA, while open-plan offices are allowed to run louder, up to NC/RC 40, roughly 45 dBA. When noise complaints start, it usually means one of two things: the equipment is generating more noise or vibration than it did when the building was designed, or the acoustic separation itself has degraded past whatever target the space was designed to hit.

Vibration transmission is often the real culprit behind a complaint that sounds like airborne noise. A rooftop unit with worn isolation mounts can transmit vibration directly through the roof deck and structure into the space below. Occupants experience that as a hum or rattle that seems to come from inside the wall, not from the roof thirty feet above them. That’s exactly what the Royal Oak tenant was hearing.

What Actually Causes an Increase in Mechanical Noise

Worn bearings increase operating noise gradually. So do loose belts and unbalanced fan blades. Nobody notices a sudden change because there wasn’t one. It’s a slow drift, similar to sensor drift in a Building Automation System (BAS). The equipment sounds slightly different every month. Staff walk past it daily and stop noticing. A tenant, hearing it for the first time in a quiet conference room, notices immediately.

Degraded vibration isolation mounts are a mechanical wear item like any other. Rubber and elastomer mounts typically last 7 to 12 years in standard installations, but that drops to 4 to 6 years for mounts exposed to weather on a rooftop, according to vibration-isolation manufacturer Vibrostop. The mounts on the Royal Oak unit were six years old, right at the edge of that window. They had lost more than 20 percent of their original static height. Vibration that used to be absorbed was transmitting straight into the building structure instead.

Why This Becomes a Lease Problem, Not Just a Comfort Problem

Persistent mechanical noise in a leased office space can become a legal issue. Most commercial leases carry an implied covenant of quiet enjoyment, a legal doctrine, recognized in both commercial and residential leases, that obligates a landlord not to substantially interfere with a tenant’s use of the space, according to Cornell Law School’s Legal Information Institute. Noise severe enough to disrupt a tenant’s ability to run calls or hold meetings can support a claim under that doctrine. A noise complaint that gets dismissed as a minor annoyance for too long can turn into a lease dispute or a rent abatement request. That costs far more than the acoustic fix would have.

How to Actually Diagnose It

A proper acoustic diagnosis starts with measuring noise levels at the source and at the complaint location. From there, check the equipment for the mechanical issues that commonly cause noise increases. Then inspect the vibration isolation mounts for wear. Don’t assume the mounts installed at construction are still doing their job years later. If a tenant has raised a noise complaint, treat it as a mechanical inspection trigger, not just a customer service issue to smooth over. That’s the mistake the Royal Oak property manager made for three weeks. The cheapest fix is almost always catching this before the tenant’s attorney gets involved.

A Few Questions Worth Addressing

Is the noise constant or does it come and go with equipment cycling? Intermittent noise that lines up with a unit starting or stopping usually points to a specific mechanical event, like a belt or a compressor startup. Constant noise more often points to a bearing or a fan imbalance. It can also mean a vibration transmission path that never fully resolves.

Can isolation mounts simply be replaced without touching the equipment itself? In most cases, yes. Isolation mount replacement is a straightforward mechanical repair. It doesn’t require touching the refrigerant circuit or electrical components. That’s why it’s one of the cheaper fixes once it’s identified as the cause.

How quickly should a noise complaint be addressed once it is reported? Treat it with the same urgency as any comfort complaint. The mechanical issue causing the noise is rarely improving on its own. The Royal Oak tenant waited three weeks for an answer that took one afternoon and just under $2,000 to fix. That gap, three weeks of an unresolved complaint against one afternoon of actual repair, is where a lease dispute starts.

Sources

ASHRAE Handbook, HVAC Applications, Chapter 49: Noise and Vibration Control

Vibrostop: Anti-Vibration Mounts for HVAC (Elastomer Mount Service Life)

Cornell Law School Legal Information Institute: Covenant of Quiet Enjoyment