hvac? oil canning

[mt0001]

i have a new house with central gas forced air and ac my ductwork flexes and oil cans mostly on the return side is ther anything wrong with puting external straps with sheet metal screws to stop the flexing and noise the builder sent out their heating guys who put a couple of straps and put some rubber between the top of the ductwork and the joist and it helped but after a few weeks the rubber looses tension so i was thinking about putting staps on the top what do you suggest
i am fairly handy

You should be able to re-enforce the duct work with no problem. Now let me explain why this is happening, and ask you a few questions. This is happening due to negitive pressure in the return side of your duct work. Just like you explained like an oil can. It might not be as simple as supporting the duct work. You might have a bigger problem at hand. Does the sheet metal have a cross break? In other words does it have a crease or several creases on large areas. How big is the duct work? How big is the unit? What kind of filter are you using? Is the filter in the unit or in a filter grill? Is your filter grill stamped face(made of one sheet of metal and louvers stamped in it) or is it a bar type(made of many bars attached to a metal frame?

yeah buck headed in the right direction with that they sell external cross breaks but is your furnace too big or is there a big couch setting in front of the return grill? the possibilties are endless on that one... maybe you should take your fan speed down one speed and check your filters

[midlantic1]

Your problem is the ductwork is too small for the volume of air your furnace is moving. Undersizing od ductwork is unfortunatly a common problem in new construction. The noise problem can be fixed with bracing but the underlying problem of undersizing will remain.

[Mike3206]

It may not necesarily be undersized ducting. it could just be the builders not using the proper guage ducting, or the installers not creasing the ductwork so that the noise does not happen. if the ductwork is not creased, there is a far greater chance of flex. Also, be sure all the return ducts are unblocked as a restriction in airflow could cause that too.