I don't have an answer but as sympathy, since I got my new furnace the air practically roars up through the floor registers!

When you say "noisy", is it whistling, buzzing, roaring, or what?

Is the noise localized at the vent, or does it seem to have a source further in?

The solution depends on what the problem is.

Basically it's when the unit is running and the blowers are running, it seems like all the noise is right there because the oil burners is right there next to it in the basement. It's a roaring/blowing sound. Didn't know if there is some sort of baffel or insulated material that you can use to maybe line the inside of the opening under the grate to absorb some of the noise or not.

You need "acoustic duct liner" ... I'm not sure if you can retrofit it or not.

Replacing that short run of duct with one with acoustic liner and an angle to prevent a direct path for sound might not be expensive.

And consider adding acoustic lining to the oil burner chamber to soak up as much noise as possible.

http://www.tuxgraphics.org/npa/air-furnace-blower-noise/ 

Very interesting lazy gardens. I wrote that down and will ask the place that installed my new duct work. They will probably think I'm nuts.

Mostly I would love noise reduction in the bedroom and the living room. I have to turn the TV up when the furnace is running, it's that loud. I might add I have an old house too with large grates. However the one in the bedroom is actually new and very small per my wishes ( can't sleep in a warm room ) plus I close it at night. Still noisy.

YOu could also try installing "high mass vinyl" - it's used inside computer cases to minimize noise. It makes the case heavier so it doesn't vibrate as much.

Not to discourage you, but, given the proximity of the furnace to the vent, you should temper your expectations about how much noise reduction you will get with such measures. It would be unfortunate if you spent a lot of effort on this and the noise moderation was too modest to make a big enough impact for you. Good luck, though.

Thanks I appreciate your comment, my expectations are definitely not high given the location but hopefully I can damper it a little without spending too much time or money.

I hope it works ouf. Please re-post if you have something done as it will be helpful for others to know the outcome.