Praise be to Allah.
This is waswaas (insinuating thoughts) from the Shaytaan, by means of which he wants to spoil the Muslims worship. It has to be ignored. The Muslim should not stop his salaah or repeat his wudoo unless he hears a sound or detects a smell, because of the hadeeth narrated by Imaam Muslim from Abu Hurayrah (may Allaah be pleased with him), in which the Prophet (peace and blessings of Allaah be upon him) said: If any one of you feels something in his stomach, and is not sure whether something came out of him or not, he should not leave the mosque unless he hears a sound or detects a smell. What is meant is that one should be certain that one has broken one's wudoo; if there is even the slightest shadow of a doubt, he remains taahir (in a state of purity).