My outdoor unit, (which I think is a heat pump as I have A/C in the summer), has started making a loud repetitive noise all night long which sounds similar to when a washing machine is out of balance. It starts about 10pm and then continues non-stop until about 6am the following day, which makes it pretty much impossible to sleep as its under my bedroom window. When the heat turns on, the sound stops for about 1 min or so, but then starts up again while the heat is still on and continues on after the heat turns off. Does this mean the unit is about to die? So far, when the heat comes on, it is pushing out warm/hot air, but I live just outside Denver, Colorado so I’m concerned about my pipes freezing if something goes wrong.

I'd have it looked at by a professional.

I've only lived in one townhouse with a heat pump. Before it died it was running longer and longer trying to keep up... and in the summer because it was running so long before shutting off the coils were icing up inside really bad.

If its dying... or needs service you'd want to know now rather than February when it's a lot colder.

Well worth the 50 bucks for a service call to a reputable local tech to come out and pin this down exactly. Service call charges can be applied to whatever solution is needed in most cases.