wa`alaykum as-salam
All praise is to Allah. Blessings and peace be upon the Messenger of Allah, his Household, Companions and followers.
1) IF YOU ARE NOT SURE that you passed wind (after performing wudu''), then you assume that you did not pass wind. [Ibn `Abidin, "Radd al-Muhtar," and Ibn Nujaym, "Al-Ashbah"]
Thus, if you are in the process of making wudu'' at the time, then you continue with your wudu''; or if you already made wudu; and had started praying, then continue with the salah. As long as it is mere doubt, and you are not certain that any wind has exited, you should not heed it, for it is likely to be Satan trying to distract you from the worship.
The Messenger of Allah (may Allah bless him and his Household and grant them peace) has said, "If any of you feels something in his stomach such that it is unclear to him, whether something has come out or not, then he should certainly not leave the mosque, unless he hears a sound or smells an odour."
[Narrated by Muslim]
And in another hadith we find:
"Satan may come to one of you in salah and blow air in his bottom, making him imagine that he has lost his wudu. So, when one experiences that, he should not turn away [from the salah] unless he hears a sound or smells an odour." [Narrated by Bazzar as in Bulugh al-Maram]
2)
IF YOU ARE SURE that you have passed wind, your wudu'' is invalidated, whether there is a smell or sound, or neither. If this happens while you are still performing wudu'', then you need to re-start the wudu''
(over again). If it happens during salah, you need to break off the salah and go and repeat your wudu.
May Allah bless you, and sustain you and us with guidance, and protect us from the designs of Satan.
And Allah knows best.
Was-salam
-Suheil Laher