CRV making a humming noise from the rear.

Could be the fuel pump. I would have your Honda dealer listen to it.

Our 2018 CRV sometimes makes a sound that reminds me of and aquarium pump running. First time I noticed it I was late at night when I was taking the garbage out. I did a bit of research at that time and concluded it had something to do with part of the emissions system purging or recycling. Don't remember the details but I concluded it was normal and annoyed as hell - it just another something of of the many things the dealer failed to warn me about.

I’ve noticed the same thing. It goes away a few minutes after I open and reclose the tailgate.

It's normal operation. See here: https://www.crvownersclub.com/threads/fuel-pump-running-when-car-is-off.193425/

I had a Civic doing the same thing, I used to say the old cow was mooing. One day I was near enough to the car I flipped open the fuel cap and wishhh air shot into tank. I realised the fuel tank needed to equalise pressure when fuel was used or expansion or pressure changes took place there is some sort of valve to release pressure or vacuum inside the tank. I requested the service center to fix it and it came back and at night it made another sound different pitch every time I open the fuel tank the air equalized and it stopped. That what I think it is. Now my CRV has a noise from the rear bumber or light area but only makes the noise on a bumpy road while in motion and I could pull out my hair.

My 2017 CRV just started making that noise. Will this drain the battery?

Hello dnadinej, If you are referencing the pump running noise, yes it uses battery power to run. If, on the other hand you are talking about the noise on a bumpy road while in motion that Guru9YVM38 mentioned, not likely. There are several drains on you car battery when it is supposedly off. First, when you shut the car off your headlights that probably stay on for a minute or two. The car's clook / radio / alarm stay powered 27/7. Then there's the pump that you likely heard. If I'm not mistaken the sensor system that acknowledges the signal from you key fob has to be 'listening' 24/7. During this pandemic, the Mrs and I have pretty much been hermits and there have been times when neither car would be used for a week on more. So, after a week to 10 days (max) we'd hop in a car and go for a half hour to an hour dirve. A couple times that meant 2 drives to nowhere - but it got us out of the house, helped keep the batteries charged, and made sure I added some fresh gas occasionlly. All in all, not a bad idea,

Honda' humming sound is normal, fuel pump sensor nothing to be concerned about according to Honda Dealership.