It’s as noisy as an air conditioner. Because it is an air conditioner — just run in reverse. Some AC compressors are noisier than others depending on manufacturer and quality.

13 year old heat pump owner here. It sounds like a normal AC running outside. It gets a bit loud in certain moments when it runs some exhaust cycle - not sure of the term for it - but that just happen sporadically here and there and lasts no longer than a few seconds.

I moved into a place with a heat pump for the first time recently and mine is definitely noisy, or more noisy than I would prefer. It's not terrible when you're inside near where it is but it is noticeable. It's also around 10 years old and I believe newer ones are supposed to be quieter.

I had a heat pump and you could barely hear it outside. I had to be within 10ft to hear it running. It could be an age thing too. Mine was installed within the past 3 years, so that probably helps too.

Like with AC units, there are quiet heat pumps and loud heat pumps.

I would look online for reviews that talk about sound. Look for information about decibels and or sones. A lot of manufacturers publish that info.

You might also want to see if anyone has published anything about the sound your models put out. That way you have a baseline number to compare new unit specs to.

I can't hear the outside unit running from inside if that's what you're wondering

We just got 2 new Carrier Infinity 24 heat pumps and I don't think I've ever heard them running (except for the fan pushing air through the ducts, but that's part of a traditional furnace too). It's an expensive system that is advertised as being particularly quiet, and I think they deliver - I haven't noticed any change in noise levels. One of them had an issue for a while so we ran the backup gas furnace instead, and I couldn't tell the difference between the one that was using the heat pump and the one that was using gas.

So it's possible to get a quiet heat pump, depending on the model.

My downstairs is heated by a cold weather heat pump, my upstairs by a furnace. In extreme cold snaps, I noticed the heat pump sound when I'm directly on the other side of the wall to it. But I can still easily tune it out and sleep with it going full blast.

We have two buildings on our property with mini split heat pumps. Both are very quiet. They can be a bit noisy indoors if you turn the fan above the medium setting. It's basically silent on the low fan setting. Low is plenty for both heating and cooling.

We have used heat pump for A/C and heat in Florida for, well, I don't know how long but the house I bought in the early 90s had one, and it was old enough we had to replace it, and the replacement lasted 20 years, so it's not a new technology.

Yes they make noise, especially when starting up, but as someone else noted, your windows are closed when you run it, it's not that loud. Not as loud as window units were.

My heatpump in my old apartment was much quieter than my new apartment with resistive heating. This one is fucking loud :(

Also, damn my power bills are way more pricy per square foot with resistive. Huge bummer.

Typically when your AC/heat pump are running your windows are closed.

If those AC units are old then they can be noisy because of their original design, bearings wearing out, or rubber dampers deterioration.

New units aren't what I'd consider really noisy. More of a rushing of air (from the fan) instead of mechanical noise (from the compressor).

Visited family for new years and slept next to one. It made about as much noise as their fridge. It's most likely a newer model.

At my mom's place

air-source heat pump, double-paned windows

I can't hear the thing at all from inside the house, and can only hear it if I go on the side of the house where it's operating, which doesn't get a lot of foot traffic. You can hear the fan there.

Generally, I haven't heard people complaining about it in the US. I have seen some people talk about it recently in the UK, which is in the middle of a push to transition to them, and I'm wondering if that's because townhouses are more-common there, with houses packed closely together.

I understand that you can get noise-reducing enclosures:

https://www.silent-mode.net/domestic-equipment.html#/

There are also water-source heat pumps. I don't know how the noise differs, but I'd bet that it's quieter, because you're moving water through a pipe rather than a lot of air. However, their installation cost is considerably higher (though their energy efficiency is also higher).

Heatpumps are in par with AC. I'm noise sensitive dye to poor hearing and sometimes turn it off to help me hear better.

You might be able to reduce the noise with some fencing or plants. Some bushes, placed where they won't disrupt airflow, will definitely reduce the noise.

I talked to a tech about it. His advice was that it depends on the type. Heat pump water heater is about sound of a stove exhaust fan, with a higher pitch. No bass.
Heat pump for room heating is lower pitch. Not bassy. But there are regs in some cities about how close to property lines they can be.

I have one a drinking water one in the basement. When I'm in the basement, it's fairly audible, otherwise can't hear it at all.

Mine isn't especially loud but my nextdoor neighbor's is.

We have a heat pump. It's a little louder in the winter, but not by much. It's very quiet other than the odd hissing sound it makes when defrosting the unit.