sounds like its under charged. Yes txv can make noise.

that is a good question. Maybe some techies can shed some light.
My heat pump system has made a slight buzz type of noise from day 1 when it is in heatpump mode. I would almost say its like a hum. It doesn't make this noise when cooling in A/C mode or gas furnace mode (I have a dual fuel system).

I have listened carefully and it is coming from the coil. I'm wondering is it because of the way the txv was installed? My txv was installed in the field and wasn't installed on the new coil from the factory?

Or could it be because slightly under charged? Length of lineset from outdoor unit to coil is about 33 feet. We added almost an extra 1 pound of R-410 I think when it was installed since the line-set was pre-charged for 15-20 feet I think.

No problems whith performace. I've tested the heat rise coming from the vents compared indoor temperature. It works good.

The humm is much more noticeable when coming out of defrost mode and the hot heat from the gas furnace is blowing over the coil just as it renenters heatpump mode. The louder humm goes away as the 'hot' heat from the furnace is blown out thru the vents and only the heatpump heat is blowing.

bus_driver...the sounds you hear could very well be coming from the txv, a faint buzz, a hiss, whoosh etc. depending how much refrigerant is being introduced into the evap. coil. It will vary as the temp of the evap. coil varies.