it's making a loud grinding noise when brewing, sounds like it's struggling, and my coffee cup is only half full

Diagnosis

The loud grinding noise and insufficient coffee volume in the Keurig K-Supreme Plus SMART are classic symptoms of a "pump cavitation" event caused by a severe blockage in the needle assembly or the internal water lines. When the multi-stream needle—the part that punctures the K-Cup lid—becomes clogged with compacted coffee grounds or calcium carbonate (scale), it creates immense backpressure. The pump continues to push water at high pressure, but because the water cannot exit the needle, the pump begins to vibrate violently and "cavitate," producing that distinct grinding or rattling sound. This is often exacerbated by the "SMART" features of this model, which precisely control water temperature and flow; if the sensor detects a flow restriction, the pump may struggle to maintain the programmed pressure, leading to a partial brew. You can confirm this by attempting a "cleansing brew" (running a cycle without a pod). If the water flows freely and silently without a pod, the blockage is localized to the needle assembly. If the grinding noise persists even without a pod, the scale buildup is deeper within the internal thermoblock or the water intake valve.

How to Fix It

To resolve this, you must perform a deep mechanical clear of the needle assembly and a targeted flush. Follow these steps exactly:

1. Power down the unit and unplug it from the wall outlet to ensure the heating element is not active.
2. Open the lid and remove the K-Cup pod. Locate the needle assembly (the gray plastic piece with multiple small punctures) at the top of the pod holder.
3. Using a professional cleaning pin or a standard metal paperclip unfolded into a straight wire, gently insert the tip into each of the small holes in the needle plate. Move the wire in a slight circular motion to break up compacted grounds or mineral deposits. Do not force the wire too deep, as you may puncture the internal seals.
4. Check the exit needle at the bottom of the pod holder. Use the same pin to ensure the bottom needle is clear of debris.
5. Fill the water reservoir to the maximum line with filtered water.
6. Perform three consecutive "cleansing brews" using the 8oz or 10oz setting without inserting a pod. This flushes the remaining debris out of the lines and resets the pump pressure.
7. Place a large mug under the spout and run one final brew to ensure the volume is consistent and the grinding noise has ceased.

If That Didn't Work

• Perform a Descaling Cycle: If the noise persists, you likely have calcium buildup in the heating element. Fill the reservoir with a mixture of 50% white vinegar and 50% water. Run the largest brew size repeatedly until the reservoir is empty. Let the machine sit for 30 minutes to allow the acid to dissolve the scale, then run 3-4 cycles of plain water to rinse.
• Inspect the Water Intake Valve: Check the bottom of the water reservoir where it connects to the machine. If there is a buildup of slime or minerals on the rubber gasket, it can restrict water flow, causing the pump to strain. Clean the gasket with a damp cloth and a drop of dish soap.
• Reset the SMART Connectivity: Occasionally, software glitches in the SMART brew settings can cause erratic pump behavior. Perform a factory reset by unplugging the machine for 60 seconds and then re-pairing it with the Keurig app to ensure the brew strength and temperature settings are at default.
• Replace the Water Filter: If you are using a charcoal filter in the reservoir, remove it entirely and try brewing. A saturated or clogged filter can starve the pump of water, creating the exact grinding noise described.

Heads Up

• Avoid "Over-Tamping": Never press down on the K-Cup pod after inserting it; this compacts the grounds against the needle and increases the likelihood of a clog.
• Use Filtered Water: To prevent the grinding noise from returning, use distilled or filtered water. Tap water with high mineral content will cause scale buildup in the thermoblock within 3-6 months.
• Monthly Flush: Run one "cleansing brew" (no pod) every two weeks to keep the needle assembly clear of residual oils and fine particles.
• Warning: Never use a sewing needle or a thick nail to clear the holes, as these can permanently widen the apertures and lead to "leaking" brews where water bypasses the coffee grounds.