Heat Pumps and Electric Heating - Is this normal?

I just noticed a slight humm coming from my Reem heat pump (outside unit) . only notice it when the unit is set to heat, but not running. It's too noisy to notice when the unit is on. When it's off or set to cool, it's totally silent, until it kicks on of course.

Is it the reversing relay for heat that I hear? Is this normal?

Thanks!
Casey

Dont know how old your unit is. Most units today the reversing valve or the SOV is not in use for heat. Just for AC
so like if it should go out in winter you will have heat.;)

Thanks for the reply!

Here is what I know of the system. The air handler (in the attic) is a York and is circa 1980. External unit is a Rheem and is dated 1984. It was put in only about 7 years ago. We knew a HVAC guy that only charged us $150 to install it when the orig. york unit failed. I noticed the humm because I had to check the wiring diag to hook up a new t-stat when ours died. (sent a signal to compressor no matter what settings you tried, even off!). According to the label in the rheem, the chageover is energized for heat. The old york was energized for Cool I guess, hense why we only had heat when the Electric Aux was activated.

All is working now, for the first time in years, but I'm kinda worried about the humm.

Thanks again!
Casey

It is the reversing valve, and likely you can reduce the humming by tightening the nut that holds the solinoid coil to the valve.

Nothing to worry about though.

Rheem is the only unit where the Reversing valve is energized in heat.

And where I live I would much rather have to run on Em Ht for a day or two for a serviceman if I had to than to go without cooling in the 105 degree 70% humidity we had last summer.
:)