What does “to shout over” mean, particularly as it has been used in a particular passage I’ve read with curious sytnax?

I don’t un­der­stand the mean­ing of shout over as it has been used
in the fol­low­ing pas­sage
from Pa­tri­cia High­smith’s novel, The Ta­lented Mr. Ri­p­ley:

A well-dressed Ital­ian greeted Dickie warmly and sat down at the ta­ble with
them. Tom lis­tened to their con­ver­sa­tion in Ital­ian, un­der­stand­ing a word
here and there.

“Want to go to Rome?” Dickie asked him sud­denly.

“Sure,” Tom said. “Now?”

The Ital­ian had a long, gray car with a loud ra­dio that he and Dickie
seemed happy to shout over. They reached Rome in about two hours and the
Ital­ian dropped them in the mid­dle of a street and said a quick good­bye.

Could some­one please ex­plain to me what to shout over means as it’s
be­ing used here?