Howdy Ags,

Seeking some advice on a newly installed HVAC system in Houston, TX. I know very little about these things.

We had a 4-ton (downstairs) and a 3-ton (upstairs) Lennox Merit system installed. We previously had a 30 year old Trane system. The new Lennox 4-ton condenser is louder at over 70 dB (buzzing sound not from fan) when running and makes a clanging/rattling sound when it turns off. It also has a crankcase heater for the compressor if that makes a difference. The 30 year old Trane system did not do this and was also quieter.

The 3-ton condenser is running great and just over 60 dB. No sound when it shuts off.

In your experience, is the 70+ dB noise level expected from a 4-ton unit like this? Is the clanging/rattling when it turns off normal as well? Would the crankcase heater contribute to the noise level or be the source of the clanging/rattling?

Thanks and gig 'em!

Regarding the clanging rattling sound when it turns off, that's often a compressor that isn't level and his hitting the sides of the enclosure after its done spinning. Make sure they installed the outside unit level. May want to also cut the power to the unit, open it up and make sure the compressor is properly secured to the frame and that it isn't missing a bolt or something like that. Compressor rattling happens a lot in fridges that get moved a lot, but is much less common in a stationary AC unit.

https://www.quora.com/What-is-the-noise-level-standard-in-decibels-db-for-air-conditioners

Currently, the 50-60 dB range is as quiet as an air conditioner can get. As of 2015, some of the quietest ACs include: Carrier Infinity 19VS - 56 dB.

At first, thought the 4T was closer to hearing, thus the problem.
Now I wonder if the 4T is a lemon ..... and the horrors of replacement are in your future.

Make sure the whole condensing unit is isolated from the pad. If they put down a prefab concrete pad, it may not be level, which can allow the whole thing to rattle on the pad. You can put rubber pads under it to help with that part of the noise.

Thanks for the replies!

Has anyone heard of a crankcase heater contributing to the noise level?

The outside units are on the same wall as our master bedroom. If they confirm everything is level and the compressor is just "loud" under normal operations, what are other options to help reduce the noise? Would anyone recommend using compressor insulation or sound cover?

Vibration during the startup that goes away quickly after is the indication of refrigerant migration to the compressor where it changes its state from vapor to liquid. The solution for this is a proper charge, and installation of the Crankcase Heater.
Ergo, IF the crankcase heater is adding to the noise, perhaps it IS faulty.
As for me, I would get a 2nd opinion NOT from anyone at the installation company. Search Google & BBB reviews.

Until noise resolution, the easiest DIY attempt to block noises to inside house would be packing all wall penetrations with an insulation that does not corrode pipes touching it OR protecting the pipes with plastic, then Great Stuff-ing/equal.

Those with ample budgets are willing to erect a masonry wall between house & HVAC to direct noises away.
They also have the cash to move the HVAC farther away from sleeping areas. Some do both.

Sorry your house planner didn't locate the HVAC outside of a closet or bathroom and away from windows.

For what it's worth, I have had Daikin, Trane, and Ruud installed in my homes over the last decade. Every single one of them has made the banging and clanging noise at shut down. I don't know what it is but every technician has told me it's completely normal and all of them are still running fine. I never figured it out. I would definitely call the installer and have it documented. These often have 10 year parts and labor warranties if the installer filled it out (he did right? Right?!) so it may be prudent to have it documented just in case.

As for the buzzing, that's usually just a refrigerant line vibrating in a wall or against a framing member. That should be pretty easy to find and stuff a piece of pipe insulation under.

Crazy, I have a Trane that is now going on 3 years old and you can't even hear it if you're 5' away in the backyard. Startup, running or shutdown, silent as can be.

Mine also ... except as a heat pump, will noise up a bit when temps drop to mid-30s or less ... of course, they all do.

Funny story about A/C noise...
Metal wall hangings may have a natural frequency close to the operating frequency of your A/C unit.

The clanging/rattling at shutoff is normal. From what I have read, it is caused by scroll compressors. They apparently spin backwards for a second when they shut off.

Thanks everyone for the replies! They were very helpful.

To close this one out, the technicians came back out and verified all specs on the unit were functioning normally. Interestingly enough, the buzzing noise we were hearing on the inside was due to some of the lines in the wall being shifted during the install. They were pressing up against the studs and the vibrations made the wall "hum." They confirmed that the compressor sounds were normal (even though louder than our prior unit) and double-checked all the readings.

Thankfully they had decent access to the lines and adjusted them enough so that the humming/buzzing stopped from the inside. Furthermore, they added sound blankets on both of the compressors for good measure. This really helped with the clanging shutoff.

For anyone getting a new HVAC install where the units are right outside your bedroom, make sure to ask your rep about noise levels and take readings before and after the install so there are no surprises!

I forgot where I came across an article but it named Lenox as one of the loudest brands out there. There is one at the coffee shop Drive though where I sometimes go and I can confirm it's insanely loud for a newer unit. I swore I would never go with them after reading it.