I have an iPhone 5s on 9.3.5 and every time I add music to the device, the files play with artifacts(glitches) on the device itself. Meanwhile the files on the computer play perfectly fine. Any solution ?
Two possibilities I can think of...
One is that the phone needs re-booting or resetting & restoring from a backup. If you keep encrypted backups in iTunes this wouldn't be too disruptive to test.
The other is that the bit-rate of the tunes is too high for it to keep up.
You may benefit from reducing the bit-rate of tunes transferred to the phone, which you can do from iTunes prefs.
The first sync after you set this will be a lot slower than normal, as it converts all the tunes to be transferred. Subsequent syncs should be back up to speed.
You are unlikely to be able to perceive much sonic difference from a phone if you down-sample to 128k AAC.