My frig makes a humming sound off and on. I can

There is either debris in the diaphragm or the diaphragm is worn out.

It's the yellow flexible part that creates the pulsing action for this vac.

Is the humming noise the sound of the motor straining to turn without moving (it won't last very long like that) or the sound of the motor turning but not operating the paddle?

Sometimes depending on what type of tire you have, they can be making the humming sound, other than that you'd have to give more detail as to where you think it's coming from, like the back or the front, the engine or the wheels, transmission?

Check the transmission fluid easy fix. The humming noise could be road noise and can't do anything about that, but if it is coming from any certain area around the vehicle would be helpful in finding a solution. Check rear wheel bearings for loose worn or damaged areas. Hope this Helps

Only when moving? Does pitch change with speed of vehicle?
Generally a humming sound from rear is a fuel pump warning you that it is getting near the end of its service life. You usually notice that more, however, when the car sitting still running and you walk around the rear of the car.
Wheel bearings can make a variety of different sounds, mostly noticed in the first half mile of driving. A "whomp whomp whomp" pulsing sound is the most definitive wheel bearing sound.
Slotted or drilled brake rotors can make a humming sound, but I doubt anyone put those on a '94 5 Series. Worn tires can get pretty noisy, but you would have figured that out if it were the problem.

Good day,
If it happens that infrequently then nothing is technically broken.
More of a design, engineering issue.
Check this. It's for a freezer but the rules are the same.

http://www.fixya.com/support/t4759036-upright_freezer_not_drain

do you ;here or feel the freezer fan working and or humming if when you open the door fan stops hold the door light switch by hand to do the same or do you hear a hum and click from behing and rear of the frig if so compressor having trouble starting

Either you have it configured incorrectly this time around, or the settings are defaulted back to original on your DVR........ adjust your DVR sound properties/settings. and check all wires/connections as well.

what you hear is the comp. trying to syart(short cycling) there is a $10 fix you can try before buying a new frig.,go to your local appliance parts store and ask for a 3in1 starter for a frig.,it has the directions right on it,let me know what happens-mike

if both sides are hot it sounds as if the compressor isnt running. pull the refig away from the wall and remove the cardboard cover the compressor is the black bowling ball loking thing that you see. fell to see if it is running should have vibration and making a humming sound. if its not running listen for 3-5 minutes to see if you are hearing an intermittent humming and clicking noise. this would indicate a bad start relay for the compressor. if the compressor is running then you mostlikely have a freon problem which will require a qualified technician to repair. good luck and thanks for using fixya Peyton..