Here are some options depending on the context:
* For peals of laughter: A roar, a volley, a burst of laughter.
* For peals of thunder: A roll, a clap, a crash of thunder.
* For peals of bells: A ringing, a chime, a clang of bells.
Ultimately, the best collective noun for "peals" will depend on the specific context and the kind of peals being referred to.