Is the sound that comes out when pressing the tongue against the roof of the mouth considered the word "la" [no] as part of the Shahada, and is there a fear of falling into apostasy because of that, especially with the presence of obsessive-compulsive disorder?

This sound that appears during the pronunciation of the word of Tawhid, or the unintentional pause on the word "Ilah" (God), does not affect the validity of the word of Tawhid nor is it considered apostasy. These thoughts are evidence of the questioner's faith. A servant's dislike of these whisperings is a sign of sound belief and strong faith, as the Prophet, peace and blessings be upon him, said: "That is pure faith." These thoughts are from Satan to grieve the believers, so one must seek refuge in Allah and turn away from them.