Expert: Greg Hughes - 2/26/2010

Question
QUESTION: I'm not sure if this is a small appliance question or an electrical issue: I just bought a Mr. Coffee MRX36 coffee maker a week ago when I noticed a faint but constant humming noise emitted from the unit while plugged into the wall. The coffeemaker was idle at the time, and I may not have noticed except for the fact that I came into the kitchen for a glass of water in the middle of the night when all was quiet. Should I be concerned? I ask, in part, because for 3 years I have owned this same coffee maker in another color and never noticed any such noise, although I can't rule out that it was there all along unless I hook it back up as a comparison. Because this is an older home, the outlet into which the coffeemaker plugs is not grounded but there is a surge protector (flat block type) on the outlet, and the aforementioned coffee maker is the only item plugged into the socket. I appreciate the help!

ANSWER: It sounds like the timer/clock may be noisy. I would take it back and replace it and see if the new one also makes the noise.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick response, Greg!

I have since taken a couple more troubleshooting steps: I plugged the MRX36 coffeemaker into another outlet on another circuit (grounded) and noted it did the same thing (humming while idle). I also dug my old unit out of storage — MRX35 same coffeemaker but another color — and couldn't hear anything until I actually put my ear up against the housing (opposite side from the clock). So it would appear that the other one I have does make a similar noise but unlike the new one it was never loud enough to have been noticed while standing a couple feet away in the three years I had it in my kitchen. Perhaps this is just a break-in issue and the humming coming from the new unit will fade with time? As I said, this is what I noticed at night when the house was quiet, otherwise it won't bother me unless it suggests some sort of hazard.

A local authorized Mr. Coffee repair center, upon being contacted earlier today, refused to speculate on the possible cause. Their customer service agent on their national line, however, stated that the noise is not normal, but again no indication if this may constitute a safety/longevity issue. My dilemma is that this is a discontinued color/model and the best they can do is either have me pay to "repair" this brand new unit at my own cost or swap it out for another color/model in replacement, which I don't need because I already own that color. My last remaining alternative is to return it to the seller who is down to the last two units, and I will incur shipping costs and restocking fees on account that it isn't technically DOA.

In order to make the best decision of less-than-ideal choices, I would like to learn whether this constant humming sound may indicate a serious problem vs a noise that I can safely ignore. In other words, what are the potential causes of this problem? For example, does the humming sound suggest that there is too little or too much electricity interacting with the components —— or is it something else entirely?

Thanks again!

Answer
From my experience I will take an educated guess, but remember I am not looking at the unit so it is a guess.

You most likely have a loose screw or another loose mechanical connection and the vibration, that is normal, is being transferred and magnified.

You may have a loose transistor or diode or capacitor or transformer that is buzzing.

In my experience noises do not disappear over time but intensify.

But I could be wrong so take what I say and come to your own conclusions. Who knows, maybe that coffee machine will work for a long time. There is really no way anyone can say for sure.