heat pump buzzing

Tried to search this, but no luck. Atlanta area, central Hvac, heat pumps oustide, air handlers in basement and attic. Yesterday temps around 75 and heat pump condenser "buzzing" but fan not moving. thoughts? thanks

Main contactor? If the compressor was trying to run and was stalled, it would likely either overheat or overload and pop the breaker. If the fan is shot, it, too would likely overheat. It might not draw enough to pop the breaker, but it would sure start to smell nasty. Once you smell burned electrical wiring, you don't forget the smell.

no breaker tripped. It seems to be running fine...it just "buzzes" every so often...do you think it is about to fail? thanks

It could be as simple as something loose and is a sympathetic vibration, or something more serious. Hard to say without being there.