The A/C of my heat pump is still working fine... but suddenly the outside unit started having this BUZZ when the unit is running. Everything seems to be working fine, the house is cool and the unit cycles nicely. Should I do something to prevent failure in the future? Thanks

This buzz is probably the contactor, if you open the panel while it is running you can detect what it is (be carefull) if it is a low voltage (24 volts) problem that can make it chatter, or dirty contacts or perhaps rusty , and yes it tells you that it is not making good contact and needs attention. Mike

Do I clean the old contactor or buy a new one? Where do you buy them?? Lowe's? Are they all the same... maybe I get a number off the old one?

You have to buy them from a A/c supply house (WW Graingers) They are sold by amp rating and coil voltage ,also the number of poles,(count the number of the bars in the contactor that move when the contactor is operated usually one, two , or three), you can get this information from the old contactor , Mike

This is a compressor problem the older the compressor the mpre warn out it gets

I have the same problem but more of a grinding buzz. They are about a minute apart in both heat and cool. I changed the contactor, but no luck. Any other sugestions?