Hello, I have a couple questions regarding a furnace noise I'm hearing during its start-up. I notice this noise has gotten louder than what it was a month ago, loud enough to make a rumbling sound which could be heard on the main floor. After self assessing the furnace I found out the rumbling noise is coming from the black disc like motor cover in the first photo. My initial thoughts was that it required manual oiling but doesn't look like there are any oil pin holes, at least not similar to the ones from oiling photos/videos I've viewed online. I don't know if anyone have experience this issue, but if you have and can help explain to me what the problem may be that would be greatly appreciated. Another question I have is more out of curiosity. In the second photo there is a round opening which is attached to the air intake, I believe that is its name. As the opening isn't connecting to anything, does it have to be closed up or should it be opened for, my assumption, additional fresh air intake? Thank you.