New answers tagged sound-proofing
1.5" X 2 feet X 3 feet or so? That's not very thick to support 150+Lb without flexing, which'll give you a drumhead effect regardless of how much foam is used. Consider putting an angle iron stiffening frame on the underside of the door. Attached firmly, it should eliminate flex, and most of the drumming.
Also, don't forget that your hinges may need to be oiled / greased well. If there's any movement of metal on metal while you're stepping on the door, you'll have a pretty strong squeak / thud that can be aggravating to fix.
What about weather stripping around where the door closes against the jamb? That is if the noise is coming from the door striking the jamb? The slap some sound proofing on the underside of it.
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