The following departmental details may be useful
Private Housing Team (for HMO matters). Email: firstname.lastname@example.org ; phone: 0117 352 1805
For a general description of the HMO licensing system and related matters, see HMO information and resources. To get information about the landlord or agents for a particular property, see How to Complain.
Neighbourhood Enforcement (includes noise enforcement). Phone: 0117 922 2500 during office hours 9am - 5pm Mon - Thu, 4-30pm Friday.
Noise complaints can be made to the council at https://www.bristol.gov.uk/residents/pests-pollution-noise-and-food/noise-complaints. However, be aware that the council has no publicly accessible response to noise at night (there are no on-call noise officers you can contact). It also expressly does not investigate so-called "one-off" events such as parties. (It claims, erroneously in my view, that one-off events are not capable of meeting the definition of a statutory nuisance for the purposes of the legislation it uses.) The only significant category of noise complaint it will deal with, therefore, is frequent disturbance from the same property. (If you're frequently disturbed by noise from several different properties—which is common in areas popular with students—that doesn't count.) The complaint process involves downloading a form with which to compile a 14-day noise diary. See Repeat disturbances for more detail.