Heat pump makes clicking noise

The heat pump in my old Kenmore HVAC system is making a loud clicking noise. I can year it from a room on the second floor. I peeked inside and there nothing hitting the blades of the fan.
Does anyone know what could be wrong? Performance doesn't seem affected for now.
Suggestions and advice appreciated.
Thank you

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.