Some person by a external microphone for the DSLR arroud $100usd ,they thought it is more worse than the built-in microphone with a lot of background noise.
Like our shotgun microphone dmm1 and wireless microphone 318c within 100USD,most often it is for the not properly used it.
1.Use the wrong cable,the accessories list always including two cable ,one is for camera and one is for the smartphone.so you use the wrong cable will take such noise.
2.The cable adapter is not connect totally successfully.a part of adapter is out of the hole.
3.Cause the dslr microphone is designed for solving the issue of long term shooting situation,so you need to stand arround at like several meters distance.
4.Any we you should choose a reliable brand ,lensgo is a good choice for you regarding the dslr microphone.