intermittent fog horn noise from underneath when taking foot off accelerator or while idle at stop light, but as soon as I press on accelerator it stops, Also rattle from under hood when car is barely rolling.
noise and rattle on 1997 Ford Thunderbird
If your speed slows when taking off it could be the catalytic converters(3). My 96 made the same sort of sound when they went out.
it sounds like it may be one of the exhaust covers maybe one for the exhaust manifold i would also check the covers under the car.