Performed the new furnace start up. No gas leaks detected. Combustion readings were normal. No CO detected in the air. Drain is working. High limit passed the safety check. Heat rise was 46°. Unit is heating properly. I indentified the rattling noise being due to not enough return air being brought in. We will need to install a register on the return drop. I left a fiberglass filter in for now to alleviate the noise. The reason for the loud noise on the initial start is the burners lighting. It’s normal, however, we can try adjusting gas pressures to suppress the noise a little bit. Everything is working properly.