Refrigerant pressure equalization.

New home came with a Bryant "builder grade" 3.5 ton heat pump. As far as heating my home goes it has worked fine.

In terms of noises in relation to the operation of a heat pump in heating mode this is likely a function of defrost of the outdoor condensing coil it also *could be* the reversing valve repositioning itself from the operation mode you put it in.

Some manufacturer's power up the reversing valve only in heating mode, so upon shut off or the end of the call for heat, this part is deenergized --- that can cause strange noises for those not used to them.

I only mention the defrost mode, because typically the odd noises during that event are more noticeable.

Thank you for the comments. I just stepped outside (19 degree weather) and the unit had no buildup of frost so I would assume the defrost mode is working correctly.

My 1-year warranty (labor) from the installer expires next May, so I want to take full advantage from it. My equipment does have 10-year warranty, which is nice.

I believe the reversing valve in ICP products (and pretty much anything other than Rheem/Ruud) energizes on cooling. So in heating mode, it's not energized and shouldn't move (most heat pumps will hold the last RV position until the mode is changed or system is turned off - they do it to cut down on the noise created when the RV changes position).

Could be the RV or, more likely, pressure equalization. Probably nothing to worry about.

I believe it varies like the wind... because?

Whether you energize RV coil in cooling or heating... doesn't change anything. My Bosch Inverter heat pump energizes the RV coil in heat mode. Seems to me a GMC heat pump I installed years ago energized in heat mode as well.

This little snippit from a training manual tells the story similarly. You have to know, that another way isn't more right than another. It's quite frequent here and else where people try to say HVAC must be done such and such way... I just point to possiblities -- of which are endless when it comes to HVAC.

"Whether you energize RV coil in cooling or heating... doesn't change anything."

Well, if the RV isn't energized, it's less likely to be causing the noise than if it were, every time it switches off.

"My Bosch Inverter heat pump energizes the RV coil in heat mode."

I'll add that to Rheem and Ruud.

"Seems to me a GMC heat pump I installed years ago energized in heat mode as well."

Goodman? I doubt that unless it was an oddity from before either of us were born!

Well, if the RV isn't energized, it's less likely to be causing the noise than if it were, every time it switches off.

True, but the noisier odd noise maker counterpart is defrost mode. Due to the length of that, that is more likely what you'll hear. Which is what I alluded to in my original post. With reversing valve position change also being a more remote possiblity... but still possible.

--It was a million to one shot, doc. A million to one.

HVAC isn't brain surgery, but some insights from a brain surgeon might be helpful here.

"When you hear hoofbeats, think horses not zebras." Dr. T. Woodward

My valve is energized on cooling. When I installed my Ecobee over the summer I had to look this information up as it was asking for this information and I had no idea.....

One piece of internet advice that really helped was setting the threshold for cooling/heating to 1.0F differential as opposed to 0.5F. Longer but fewer cycles. Hopefully my electric bill reflects this, I read my compressor requires 100A on startup.

My valve is energized on cooling.

cobalty2004,Irony is a dish best served cold. Thanks for clearing it up...

The noises you are hearing are related to defrost mode as I initially thought.

Yet, the builder is ready to call a brain surgeon. Maybe he should take his own advice...

Yes, the noises are most likely related to defrost mode which is the most probable explanation and the one you'll get if you do a simple internet search. A heat pump's reversing valve shifts in defrost mode, so that's not a separate root cause it's all part of the switch to defrost mode.

When troubleshooting a problem, start with the most likely cause before exploring less likely causes. That' the point of the hoofbeats wisdom, Ray.

"A heat pump's reversing valve shifts in defrost mode, so that's not a separate root cause it's all part of the switch to defrost mode."

Good point, forgot about that!

I'll still keep my ears/eyes on the thing throughout winter.

I am amazed however on how much heat the thing can produce even in 20 degree weather.

"I am amazed however on how much heat the thing can produce even in 20 degree weather."

Just keep an eye on the thermostat, make sure the AUX heat isn't coming on - that gets expensive!

LOL Charles.

The reversing valve change is a brief moment... plenty of other noise producing events during the whole time a heat pump is in defrost mode. There is more to defrost mode on a heat pump than merely switching the reversing valve back and forth. Brain Surgeons stay on alert...

If you're not right on top of the unit / unit isn't placed near a window like all MFG's recommend 9 times out of 10 you'll miss it in favor of longer lasting noises during defrost mode. They call it defrost for a reason... a traditional air conditioner does not have a defrost mode.

Now if the unit is placed under, in front of or near a window due to 'builder grade telepathy' (you know "contractual obligations" among middle men festivals) then all bets are off.

What other noises are there?

The fan will turn off briefly correct?

The outdoor fan should not operate in defrost mode because it's self defeating. You should hear the reversing valve reverse (usually a "schwoosh" sound) and compressor. I could hear my neighbor's heat pump from 100 feet away when it went into defrost mode.