Hum coming from Turntable

I need help in tracking a slight hum on my turntable.   I did narrow it down, and the cause of this would be my turntable.   Is this due:

1) cartridge not grounded properly 
2) cartridge wires are loose
3) turntable grounding is bad 
4) phono cable not properly shielded

Can any members/technical person that work on turntable can help me out.  Much appreciated!
Also add:
5) Magnetic fields caused but inductance loops from household wiring.
That one took me a couple of hours to figure out once. But one should rarely find that if the house is wired with Romex.

Does it do it whether the TT motor is running or not? 
1) Does the cartridge even need to be grounded? The two wires come off if each coil
2) doubtful to be causing a hum
3) Seems the most likely to me

4) I would doubt #4 unless the RCAs were running along side of a power line going into the TT.
holmz… my household grounding is excellent, all of the ground are properly attached.  
Motor and speed controller are both unplug, i still get a hum noise.  
Fyi… i am using a Forsell Air Reference and Air Tangent tonearm.   The table materials are acrylic and wood, and the tonearm is made of plastic and aluminum with Rca output for the Tonearm.  
The Google Wifi was causing a hum for me.  Had to move it farther away from the turntable.

Broken ground inside tonearm was also a cause at one time.

@zipost it has nothing to do with you household grounding.It is likely a magnetic field if it is 60 Hz.
But it could also be a ground loop.
Has this hum always been present, or did it recently appear?
What are you using for a phono stage, and how did you establish that’s not the problem?
Cleeds….just bought the TT recently, i had 3 phono stages to swap out to see if i can back track the problem, with the same results.  It’s for sure the noise is coming from the TT or phono cable. 
Just how loud is the hum? How is your TT connected to the phono stage - balanced? Unbalanced? What cartridge are you using? Have you tried another?
My hum was solved by using better shielded RCA cables.

Easy to diagnose if you have spare RCA's to try out.  
My tonearm wiring insulation became worn, made a slight intermittent hum, wiggled the wire, found it, being re-wired now.

you can use any common wire for a separate ground wire, thus you can substitute any interconnect cable you know does not hum to prove your phono cable is not the problem (or is, unlikely). you can use the phono cable for an interconnect (omit the ground attachments, another way of proving it’s not the cable.

cartridge wires: while on, simply touch end of joint of the wire on the pin (making a good connection) with a small plastic handled screwdriver. one at a time. hum changes? goes away? then remove with needle nose pliers, tighten, re-install. Or, just remove/tighten/reattach, never hurts to be sure.

keep in mind: whenever you move a cable or any piece of equipment, the other end? adjacent cables both ends?

The simple answer to your question is yes. All of the above can create hum. Usually it is a ground loop somewhere. Is it a high sound buzz or actual low pitched hum? If the latter, that is a ground issue usually. You didn’t mention your phono stage or other equipment. If tubes are in the mix anywhere that can be your source of noise. If low enough to not be heard with a low volume sometimes it can be lived with. Chasing down a hum can be nightmarish. As mentioned, try different cables first, possibly even the PC if that is possible. Make sure you don’t have any wall warts in your power system. Could also be your phono stage settings or cart in general. Lots to play with. Good luck!
Thank you all for the awesome advise, it helps alot.  I want to ask if the body of all cartridges has to be grounded or certain cartridges doesn’t need the body to be grounded to the head- shell?  Also, can i say that all turntable tonearm & base has to have ground loop with the turntable body?   What happen if just the turntable by itself has a ground loop but the tonearm doesn’t or vice vera?   Will this cause hum noise?  
I would run all grounds to the same point.
If the cartridge is plastic or wood, then I am not sure how grounded they are??

If it is inducted field, rather than a ground loop, then it can get more complicated… but moving the switching supplies to another power strip might provide a data point?
Try this. Gently move your cart wires a bit with your finger when everything is turned on and the tone arm is “home”. See if that changes anything. I had ground issues for quite awhile and found that I had to have anything the turntable was connected to plugged into a single outlet via a power block of some sort. I currently use a Shunyata hydra which is great. Overall though, the ground issues I had related to the phono stage and it’s position relative to the tone arm. 
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What happens when you disconnect the cartridge at the cartridge, first with clips isolated then with both channels shorted to their ground leads?

Try different cartridges to see if they are all affected similarly. Try grounding yourself and moving your cupped hand around the cartridge.
If the hum changes the cartridge is not well shielded.

The tonearm ground should be connected to the turntable which in turn should be connected to the phono stage. You can try floating the ground on your preamp with a cheater. I have an IEC power cord that has had the ground plug pulled off the male end I use for such occasions.