Electrical buzzing on MacBook Pro case when plugged in

Figured out what was "wrong". The EMI filters leak current onto the case. If you use the 2-prong plug on the charger there is not a ground to remove the leakage current. So you can become the ground. You also act as a capacitor to ground when you touch the case, and this extra capacitance from you add increases the leakage current. The currents are low, from between 5-50 microamps. I also measured voltages up to 46V. This is all at 60 hz. But the weird thing is that you only feel a buzzing sensation when you are moving your fingers on the textured part of the case surface. If you stop or move over the smooth apple logo on the top of the lid you cannot feel it. I also tested this out on two other new MacBooks Pros in the apple store with the same effect. The apple tech also felt the same thing so it's just not me. I tried it on a MacBook Air and got nothing. I see this more as a nuisance if I'm working on my laptop and I feel this constant buzzing on my hands as they rest on the case as I type on the keyboard. The simple solutions are either 1) Use the 3-prong cable to your charger so the case now has a good ground 2) Wear shoes so you are not grounded, assuming your floor is a good ground or 3) Don't work on it while its plugged into a 2-prong charger.

I found the same affect on two other M4 MacBook Pros in the Apple store and the store tech felt it to, so its just not me. So I assume it applies to all the new M4 Mackbook Pros. The levels of currents are extremely small, well below acceptable safe levels. I think the limit is 500 microamps. I measured from 5-50 microamps depending on how much body surface area touches the case...finger tip, palm or arm.. I measure the same level of leakage current on my other Mac laptops too, but I only feel the buzzing effect on my M4. I've now read that others have felt the same thing on posts from 10+ years ago.

From using ChatGPT to do some research I came to the conclusion that the EMI filters that are used to filter out noise will let 60 hz leakage current through to the case. This is what it is supposed to do. So if you touch it and you are also grounded, thus completing the circuit, you are then adding additional capacitance to the EMI circuit so even more current can leak onto the case. Most people are not usually grounded. In my case, the copper radiant heating pipes in my concrete slab provided a good grounding path and I had my shoes off which completed the circuit to ground that gave me the buzzing sensation.

Now I don't get this effect on other cases, so it's something to do with the M4 case. I measured that none of my Mac laptop cases are conductive, which doesn't surprise me since it's anodized aluminum which is non-conductive. So all of this involves completing circuits capacitively at 60 Hz. I also only get it while moving my fingers. If I stop so does the buzzing. If I do this on the smooth apple logo on the top of the case the buzzing also stops. It a weird effect. I just happen to have the all the right conditions to be able to ground myself without trying. Most people will not be grounded enough to feel this. At the Apple store I had to ground myself to the ground socket of the AC outlet. I used my multimeter to do this and know enough not to stick it in the hot or neutral socket. FYI my case is the Space Black color and screen is the new anti-glare...don't know if this makes a difference.

I also wanted to add that my house grounding situation is probably more unique, such that most people will not encounter this problem. I have copper pipe radiant floor heating, which I guess does a good job at capacitively connecting me to ground. When I was at the apple store the floor didn't ground me at all, so I had to ground myself to the AC outlet ground to feel this effect. I've also now seen people encountering this problem in the past. In the past I was charging my laptops via different adapters from an old Apple monitor, which is grounded. With the new MBP MagSafe connector on the M4 I didn't have the correct adapter anymore, so I've been using the a 2-prong power adapter. This is probably why I never noticed this before.

I've also found this effect has disappeared on my M4 MBP, with the only difference being that it's actually charging now (amber led) because I let the battery get down to ~50%, when before it was fully charged (green led).

For comparison when I do take my old MacBook Air and charge it with the 2-prong adapter, I can measure the same level of leakage currents and voltages through me but without the buzzing/tingling feeling. Unlike my MBP it's actually in charge mode (amber led) and I measure these. I had the same thing happen in the apple store with the tech's MacBook Air. So there is still some weird combination of materials/coating process/texture on the case and maybe the EMI filters that has been different over the years.

I found the same affect on two other M4 MacBook Pros in the Apple store and the store tech felt it to, so its just not me. So I assume it applies to all the new M4 Mackbook Pros. The levels of currents are extremely small, well below acceptable safe levels. I think the limit is 500 microamps. I measured from 5-50 microamps depending on how much body surface area touches the case...finger tip, palm or arm.. I measure the same level of leakage current on my other Mac laptops too, but I only feel the buzzing effect on my M4. I've now read that others have felt the same thing on posts from 10+ years ago.

From using ChatGPT to do some research I came to the conclusion that the EMI filters that are used to filter out noise will let 60 hz leakage current through to the case. This is what it is supposed to do. So if you touch it and you are also grounded, thus completing the circuit, you are then adding additional capacitance to the EMI circuit so even more current can leak onto the case. Most people are not usually grounded. In my case, the copper radiant heating pipes in my concrete slab provided a good grounding path and I had my shoes off which completed the circuit to ground that gave me the buzzing sensation.

Now I don't get this effect on other cases, so it's something to do with the M4 case. I measured that none of my Mac laptop cases are conductive, which doesn't surprise me since it's anodized aluminum which is non-conductive. So all of this involves completing circuits capacitively at 60 Hz. I also only getting it while moving my fingers. If I stop so does the buzzing. If I do this on the smooth apple logo on the top of the case the buzzing also stops. It a weird effect. I just happen to have the all the right conditions to be able to ground myself without trying. Most people will not be grounded enough to feel this. At the Apple store I had to ground myself to the ground socket of the AC outlet. I used my multimeter to do this and know enough not to stick it in the hot or neutral socket. FYI my case is the Space Black color and screen is the new anti-glare...don't know if this makes a difference.

I did hook a scope to up. To begin my laptop is pretty electrically isolated by sitting on a glass top desk. There is not much stray capacitance nearby either that could ground out an AC signal. The signal I measure is 60 hz and is the typical distorted shape you might expect from a power supply. The case by itself goes to a peak voltage of ~0.4V relative to earth ground. While I by myself go to about a peak voltage 1.5V. However, when I touch the case, I go to peak voltage of between 25-30V! (It maxes out the input of my scope at 20V). It only takes about 1mA at 60 Hz to feel a tingling in your fingertips and this is enough voltage to drive 1mA through my body resistance.

So is this laptop defective, or is this an issue with all recent MacBook Pros? I never noticed this with my old MacBook Air or M1 MacBook Pro.

Thanks, I did have one in my drawer of old apple cables, of which the iPhone lighting connector cable will eventually join. I'll probably just windup grounding it through my USB-C connection to my second monitor which is grounded by a 3-prong plug.