I thought I read the reason behind this awhile back on this forum, but can not find the answer again. 

I know it’s not defrost cycle because defrost lasts longer than this draw. It occurs almost every 4 hours (didn’t realize that until now) for 2 minutes. I thought I read that it’s the compressor ramping up high speed to spread the oil/refrigerant throughout the system. It doesn’t seem to happen when there is a bigger constant draw. Like when it’s cold outside and high demand in the house where the system is running most of the heads for a longer period versus when it’s 45* outside and maybe 1 head is calling for heat. 

I’m not overly concerned, but what annoys me is when the system ramps back down it creates a loud “whistle/hum” from the ODU. You can hear it at night really bad (I know because the house is quiet) and may wake you up. It still happens during the day, but less caring because of the daily activity going on. 

If anyone remembers (probably not because I’m not on here much) I had an issue with one head not operating correctly and causing system to go into error mode in the summer. I thought it was low refrigerant because of the code. Ended up being I miswired 2 of the heads in the branch box. Simple swap them correctly and everything has been great.