Strange little pinging sound from heat pump

[Siffleu]

since having a heat pump is new to me, I would like to know if I should call someone to check my heat pump because of a little pinging noise (like a popcorn into a can) that seem to came from the compressor on the exterior unit. I got it installed for about a month now. It's a Carrier 38QRF018 with a 40QNQ018. I had a look on the exterior unit and it's frosted. 25 F outdoor and indoor unit set to 66 F.

thanks

edit:had it stop for 15minutes, restart it, same sound came after few minutes... had it stop again 15min went to cooling mode, had the exterior coil defrosted a bit for 15minutes, stopped 30 minutes, turn back on heating and no more pinging sound but came back hours after...