Installed an rth2510 and installed as labeled on old stat and sounds like my ac nut is buzzing outside, any thought?

Question: do you have a multiple thermostat setup in 1 zone? If so check what settings are for your heat on each thermostat. Make sure that the heat is not set higher than the room's temperature.
check what settings are for your cooling on each thermostat. Make sure that the cooling is set accordingly.

if you have multiple thermostats setup in 1 zone. the thermostat with the lowest temperature will reign supreme. The heat setting on that thermostat will be what's causing the buzz on the heater.

optionally, hard reset your thermostat as a precaution. Here's how to do so: there are two types of thermostats i know of programmable and non-programmable.

disable auto & enable manual; however do NOT change settings or power-off t-stat. Remove battery and power down the thermostat until you see nothing on the thermostat monitor; power OFF the switch connected to your t-stat. Remove battery and reinsert inverted, if needed, press whatever button that your heart desires to make sure that nothing is absolutely drawing into that mode, button, etc; wait (5sec-1min); remove batters; wait 1min; then, reinsert batteries in its correct position; if you have a programmable thermostat; do the same with the hit 'reset filter' held down observe if the roomTemp reading has changed.

May I suggest to keep an extra thermometer around to determine if temperature reading accurately?

If reset requires a reprogramming to your t-stat, do whatever required to set your desired setting.

cheers, best of luck. i hope i've helped.

background, doing a hard reset in my opinion is similar to removing the battery from a PC motherboard.