@skyy92677 Hum always occurs at the powerline frequency 50 or 60 Hz, depending on your national standard. Ground hum is always the result of an imperfect ground causing a resistance, and thus a current to flow. Induced hum is also due to an imbalanced induction of AC onto an otherwise unconnected wire pair.
This is why balanced inputs tend to be quieter - noise induced on both lines is cancelled by the inverting input. This is known as CMRR - Common Mode Rejection Ratio. Common mode rejection ratio is the measure of a device’s ability to reject the signal common to both the positive and negative device inputs, specifically, a differential op-amp. Fun Fact: The differential op-amp was invented 20 years before the transistor for use as a long distance telephony signal repeater. The patent was rejected for 10 years because the patent clerk didn't get how they could work, but was finally granted in 1938.
So, now you know what you're looking for - either a grounding issue or an induced hum possibly by a wire pair closely adjacent to an AC line. Adding more grounding points is likely to cause more hum not less, and is a code violation. Double grounding, or grounding at multiple points in a system, can be hazardous and lead to safety issues. It can create parallel current paths, potentially leading to electrical shock hazards, fire risks, and damage to equipment due to circulating ground currents. I agree: find yourself a new electrician.