well, it's not Ffrydaye, and this actually does kinda sorta maybe relate to
buses ...

my brother got this from their Tech Line (dealer mechanics call the
manufacturer help line when stumped with a problem, especially on newer
cars).

Describe that noise when you call Tech Line

Identifying noises is one of Tech Line's biggest challenges because every
customer, advisor, and technician can have a different description for the
same noise, and these descriptions usually don't match the ones in Tech
Line's database. To get an accurate repair from Tech Line when you call in
with a noise complaint, and for accurate noise descriptions on warranty
claims, use one of the sounds from this list:

Noise                         Description (sounds like)
-------------------            ---------------------------------------------
------------
Banging                     Slamming a wooden screen door
Bonging                     Hitting a large gong
Booming                    Rumble of distant thunder
Buzzing                      Electric razor

Chafing                      Rubbing dry hands together
Chattering                 Windshield wipers across a dry windshield
Chirping                    Bird or cricket call
Clacking                    Railroad car wheels rolling on a track
Clanging                    Cow bell or dinner bell
Clanking                    Wrench dropped on concrete
Clapping                    Hands clapping
Clashing                    Cymbals hitting together
Clattering                   Falling bowling pins
Clicking                     Empty bottles hitting each other
Clunking                    Slamming a heavy wooden door
Cracking                   Ice cubes breaking when dropped in water
Crackling                  Wood burning in a fireplace
Creaking                   Opening a door with rusty hinges
Croaking                   Frog call
Crunching                 Walking on dry snow

Droning                    Distant propellor-driven airplane
Drumming                Nervous fingers tapping a desk

Fluttering                  Flag flapping in the wind

Grating                     Shovel raked over pavement
Grinding                   Sharpening a tool on a grinding wheel
Groaning                 Twisting wooden beam on a ship
Growling                  Dog protecting his food
Gurgling                   Water down a bathtub drain

Hissing                     Leaking Tire
Hooting                    Owl call
Howling                    Wind blowing through a leaky door
Humming                 High-voltage transformer

Jingling                     Keys hitting each other

Knocking                  Knuckles rapping a wooden door

Moaning                   Blowing across the top of an empty bottle

Oil canning               Flexing a metal gas can

Pattering                  Rain drops hitting a window
Pinging                     Pebbles rolling around in a tin can
Popping                   Cork coming out of a champagane bottle
Pounding                 Hitting your fist on a desk

Rapping                  Judge using a gavel
Roaring                   Speeding 4x4 truck with open-tread tires
Rumbling                 Bowling ball rolling down an alley

Scratching               Rubbing two pieces of paper together
Slapping                  Dribbling a basketball on a hardwood floor
Squealing                Skidding tires

Ticking                     Tapping a pencil point on a desk

Whining                    Distant siren
Whistling                  Steam coming out of a tea kettle