Probable cause is mineral scale on the heating element. It's a common issue with hard water.
You need to descale the brewer. Scale is non-toxic but hinders performance and can cause noise.
- Get 8 oz undiluted white vinegar and a 10 oz ceramic mug.
- Fill the hot water tank to the FILL LEVEL with vinegar.
- Place the mug on the drip tray, close the lid, and perform a brew cycle without a K-Cup.
- Pour the hot vinegar from the mug back into the tank. Let it sit for at least 30 minutes.
- Perform another brew cycle without a K-Cup, emptying the mug into the sink.
- Flush by running three full tanks of bottled water through brew cycles without a K-Cup.
If that didn't work: If the noise persists after two descaling attempts, contact Keurig Customer Service. The internal parts are not user-serviceable.
Heads up: Descaling every 3-6 months is recommended for optimal performance. Use filtered or bottled water to slow scale buildup.