You're on the right track with the capacitor replacement. That's a good first step, especially given the symptoms you describe. Here's a breakdown of possibilities and what to investigate further

Likely Causes (in order of likelihood, given your description):

1. Capacitor Failure

You're already addressing this. A failing capacitor can cause all sorts of weird noises and performance issues in a capacitor-run motor. It can lead to:

Reduced Starting Torque

Even though it's running, the motor might be struggling to overcome its own internal friction, causing the noise.

Phase Imbalance

Capacitor-run motors rely on the capacitor to create a phase shift between the starting and running windings. A bad capacitor disrupts this, leading to unbalanced currents and potentially noisy operation.

Harmonic Distortion

A faulty capacitor can introduce harmonic distortion into the motor's current, which can cause vibration and noise.2.

Winding Faults (Less Likely, but Possible)

While the motor runs, there might be a partial short or winding insulation breakdown. This is less obvious because the motor still works, but it can cause:

Arcing/Humming

This can manifest as a grinding/growling sound.

Overheating

Check the motor temperature after it's been running for a while. Is it excessively hot?3.

Motor Mounting/Vibration

Even a perfectly good motor can make noise if it's not properly mounted.

Loose Mounting Bolts/Screws

Check that all mounting hardware is tight.

Resonance

The motor's vibration might be amplifying due to the way it's mounted to the unit heater. Try loosening the bolts slightly (just enough to feel a slight play) and then re-tightening them. Sometimes a slight change in torque can dampen the noise. Also, check that the motor is not contacting anything.

Damaged Rubber Mounts

If your draft inducer is equipped with rubber vibration dampeners, inspect them for cracks and dry rot.4.

Induced Voltage/Current in Nearby Components

Rarely, strong magnetic fields from the motor can induce voltage and cause vibration in nearby metal that is not mechanically isolated.

Troubleshooting Steps (Beyond Capacitor Replacement)



Check Voltage at the Motor

Ensure the motor is receiving the correct voltage. Low voltage can stress the windings and potentially cause noise.

Current Draw (If Possible)

If you have a clamp meter, measure the current draw of the motor. Compare it to the motor's nameplate rating. Excessive current indicates a problem.

Visually Inspect Windings (If Accessible)

Look for any signs of burning, discoloration, or insulation damage. This usually requires disassembly.

Megger Test (If You Have a Megger)

A megger (insulation resistance tester) can detect insulation breakdown in the windings, even if it's not visually apparent. This should only be done by someone familiar with high-voltage testing.

What to Consider Before Replacing the Motor



Cost

What's the price of a new draft inducer motor? Factor in your time for installation.

Age of the Heater

If the heater is old, other parts might be nearing the end of their life. Consider whether it's worth investing in a new motor for an aging unit.*

Availability

How readily available is the replacement motor?

Before Replacing Anything (Again, After Changing the Cap)


Thorough Visual Inspection

Use a flashlight to carefully inspect everything around the motor. Look for anything that might be rubbing or vibrating.2.

Sound Dampening: Try holding different parts of the draft inducer assembly while the motor is running. Does holding a specific part change the noise? This can help you pinpoint where the vibration is originating.Good luck! Changing the capacitor is a smart move, and hopefully, that will resolve the issue. If not, methodically work through the other possibilities. Flag for review