birring
bombilation
bombinating
bombination
booming
burring
buzzing
drone
gabble
gibber
gibbering
hum
humming
jabber
jibber
low rumbling
maundering
monotone
monotonic
mouthing
mumble
mumbling
murmuring
mutter
muttering
purring
soniferous
sonorous
sounded
sounding
susurration
thrumming
tonal
toneless
whirring
whisper
whispering
whizzing
intonation
modulation
pitch contour
Trilling
atonal
beep
buzz
cheeping
chiming
chirruping
chittering
churn
dirge-like
drip-drip
everpresent
low-pitched
mewling
plash
singsong
soughing
stridency
throb
thrum
whirr
whispery
whoosh
bemoaning
boning
cloning
condoning
groaning
honing
intoning
loaning
moaning
owning
phoning
postponing
rezoning
stoning
toning
zoning