If the noise changes in pitch or intensity when the engine RPM changes, it's probably some type of engine noise, and interference from the alternator output is a likely source.
Ọ bụrụ na mkpọtụ ahụ gbanwere ma ọ bụ ike mgbe ígwè ọrụ RPM gbanwere, mgbe ahụ, ọ bụ ebe nchekwa dị mma na ị na-eme ụdị ụzụ ígwè, na nnyonye anya site na mmepụta onye na- emepụta ihe bụ isi iyi.