Diurnal: happening by day, coming out during the day, occurring every day.Also animals which come out at twilight are called crepuscular.
The opposite of nocturnal is diurnal. Diurnal is from the latin "diurnalis" which comes from "dies" (day).
Check your tires for proper inflation and balance, this is the only the first step, you could also have loose lug nuts or worn front end parts.
More likely birds, but rats are possible if they are using your car to get up to somewhere high.
The term opposite of nocturnal is "diurnal." (active mostly during the day). The opposite of nocturnal is diurnal.