From time to time I stand in line to pray (saff) beside people who are loud while we are praying. Sometimes it can be annoying when we are in sujud to hear other voices. Is it permissible for me to draw his attention to the fact that his voice is too loud and that he is impeding me while I pray?
I think it is right to tell the person if it is disturbing your prayer.
This is a verse from the quran that states we should use a proper tone depending on the situation.
Say, "Call upon Allah or call upon the Most Merciful. Whichever [name] you call - to Him belong the best names." And do not recite [too] loudly in your prayer or [too] quietly but seek between that an [intermediate] way. [Surat Al-'Isrā' 17:110] (Sahih International)
So we must follow that.
You should warn him politely after he finishes his prayer. Don't draw his attention while he is praying. It may disturb him. Read the following fatwa for more.
One of my friends while offering sunnah namaz recites surah in a little loud voice that I can easily hear his recitation and get disturbed in my namaz. What should I do?
Ask him to recite in the same volume in sunnah salah as the others do. If he follows it then it is ok; otherwise you should offer sunnah at a distance from him.