I recently added a second story to my existing ranch. I put a second zone for the second floor, and left the first floor as is.

My return on the first floor opens up at the floor level on a wall and is approx. 24"w x 14"h. I used to have a baseboard cover, but it got thrown out. I went to the store and brought a "flat" one and installed it. The noise is incredibaly loud... nobody can hear anyone talk, and I have to turn the TV volume up high.

Should I have gotten one with a damper on it? I think my old one had one. And should I have replaced it with another baseboard cover, not a flat one? There is a 1/4" gap where the floor meets the cover, and if I had a baseboard cover it would cover this up. Any ideas?

You said that the original return was a 24 by 14 inch return... If you down-sized the area to less than that with your new return grill / cover you will cause the condition of noise due to the air trying to now move through a restricted size opening. If the original is a 24" x 14" the new grill must be the same size. ( As well, the return grills are different than a feed register in air flow design and construction )

I recently added a second story to my existing ranch. I put a second zone for the second floor, and left the first floor as is.

My return on the first floor opens up at the floor level on a wall and is approx. 24"w x 14"h. I used to have a baseboard cover, but it got thrown out. I went to the store and brought a "flat" one and installed it. The noise is incredibaly loud...nobody can hear anyone talk, and I have to turn the tv volume up high.

Should I have gotten one with a damper on it? I think my old one had one. And should I have replaced it with another baseboard cover, not a flat one? There is a 1/4" gap where the floor meets the cover, and if I had a baseboard cover it would cover this up. Any ideas?
Visit your local sheet metal shop and have them *build* you something similar to your baseboard cover. It shouldn't cost that much, and you can draw it up on paper and have them build your design. It won't be as expensive as it sounds, but it's a custom touch that will achieve your purpose quickly-and you know it works!