Rumbling sounds can be an indication of sediment buildup at the bottom of your water heater. This can lead to trapped water boiling which affects the efficiency. To help dissipate it, you can attach a drain hose to the valve and let it run for about five minutes. Newer models offer protection against this, but if you have an older one, it may be worth replacing entirely.
Miami 24/7 Plumbing offers year-round maintenance to assist with this issue.
Remember: hot water is dangerous! Discharge it into a floor drain, laundry tub or bathtub, and make sure you turn off the power before draining.