The Romans did not bury their dead in mounds, but in the 4th century B.C., the Etruscans were still very much around, using tumulus tombs. The rich had whole rooms organized for the comfort of their spirit, such as those at Banditaccia (7th-6th century B.C.), others simply buried the ossuary into a solid mound of earth.
The Etruscan tumuli were normally family tombs that were used for many generation of the same noble family, and the deceased were buried with many precious objects that had to be the « grave goods » or the furnishings for these « houses » in the Afterlife. Many tombs also hold paintings, that in many cases represent the funeral or scenes of real life. The most important graveyards (necropolises) with tumulus tombs are Veio, Cerveteri, Vetulonia, Populonia.
With all those burial mounds clearly visible in the regions Rome was gradually taking over, one can easily imagine bands of youths who had a little too much to drink go to the trouble of punching through the door (or wall) to have a little late-night party with the deceased. Sure the Romans were superstitious, but that only makes it more fun.
Lots of pictures of Etruscan tombs, artefacts and buildings at Georgia University (Athens!).
These few pages of Etruscan Italy by John Franklin Hall provide interesting details about the practice.