How large is the duct, how is it routed (straight out the back, up and 90 degree bend, etc), and how far is it from the hood to the Abbaka?

A silencer will be about 3 feet long, and about 4 inches larger in diameter than your duct. It should make a significant, if not tremendous, difference in sound level.

Maybe something is loose and rubbing the squirrel cage in the blower, or some other mechanical failure. That might be evident if the cover can be removed for inspection.

I see on their web site that Abbaka has a 7 year warranty, in case that helps.

As far as more insulation, search gardenweb for "dynamat", which is a thin ( about 1/15th inch) rubber/metal foil product, most often used inside car door panels and trunks to decrease road noise and fix rattles, but can also be wrapped around your duct. I don't think you need that much coverage to dampen out some of the tinny vibration transmission, if that is what you have. It is rather pricey, at about $5/sq ft.

This post was edited by attofarad on Thu, Jan 3, 13 at 22:30

My only experience is with Ventahoods so I don't know how yours is constructed. Before undertaking any reconstruction, a few things you might check: if you have dampers (most hoods do) I'd check them, especially if one set is near the intake by your baffles as well as your outside damper. You don't mention any mechanically related noise and if a damper has become stuck the increased turbulence will increase the perceived loudness of the airflow. We had a similar issue with our VH.

OP has modernaire not VAH

I think the key here may well be the proximity of the Abbaka 1400 cfm blower to the insert, if the insert is on an outside wall and the blower is 6" away that could be the problem.

Silencers, or mufflers, use acoustic techniques just as your car muffler does, to reduce noises from upstream, in this case noises such as fan blade tip air turbulence. In addition to fan blade induced noises, and motor bearing noises, turbulence in the ducting can also add noise. None of these should change over time.

What can change over time is rattling of loose ducting, along with the aforementioned problems that could occur in the fan housing, like a squirrel in the squirrel cage.

Dynamat, and similar automotive body-shop products, are used to damp vibration in sheet metal, and can be effective in reducing conducted fan motor noise and turbulence induced rattling or vibration in the ducts themselves.

Beyond fixing whatever is obviously now wrong with your exhaust system, whatever you do that fits to reduce vibration and noise will pay off in reduced tension.

kas

hollylh, the dynamat, if used at all, would be in addition to a silencer. It would dampen out some of any vibration noise of the duct. I don't plan to install any myself, but my duct will be fully accessible in the attic after installation, in case I want to modify anything. If you have ever heard water noise hitting a plain stainless sink, vs. one with a 4 inch square of rubber glued to the bottom, you have an idea of how a small bit of damping can reduce noise considerably.

I got my Fantech LD10 at homeperfect.com; I see that they have it for under $150 delivered.

The LD10 is 14 inches in diameter, so there is a chance that it will not fit in your ceiling between floors. Even the 8" duct LD8 is 12.5" in diameter.

You may find that the way the duct/blower were mounted could be improved. e.g., by having rubber isolation in the mounting/strapping, etc.

Here is a link that might be useful: Fantech silencer specs

If I understand your info correctly, you have a vertical run up an inside wall, and then a horizontal duct run through the kitchen ceiling to the outside. I'm no HVAC expert compared to others who contribute here regularly, but I have discovered through my research that duct size dramatically (and inversely) affects the air flow velocity which directly affects noise. You did say the system was noisy to begin with, so I'd be curious about your duct size once it does get exposed. Would you be willing to post the dimensions in your followup? The Wolf Ventilation Guide recommends a 10" diameter duct for a 1200 CFM external blower. This is mathematically equivalent to about a 4" x 20" rectangular duct in cross sectional area.

Since you will have an opportunity to open up the ceiling, please make sure to check the following:

1.) Duct size - critical. An undersized duct will definitely make the airflow lower and the noise higher. If the hood mfgr requires an 8" or 10" duct, and you have a 6" or 7" - "there's your problem right there".

2.) Duct material - if there's any section of the duct that's made of flexible ducting - "there's your problem right there".

3.) Joints - improperly sealed joints can loosen over time, leak air, and vibrate.

4.) Less likely but still possible - grease buildup / foreign object obstruction in the duct.