I grew up in a Catholic Charismatic household, where I heard tongues on a regular basis. Tongues basically sounds like gibberish, and can be spoken, chanted or sung. People unfamiliar with it can find it really odd, but growing up with it it was normal to me. I remember even as a kid attending a Junior High retreat, and coming home thinking that maybe I had gotten the gift of tongues. My Mom asked to hear it, and I chanted "Hmmm mama hmmm papa", and she encouraged me hold back for a few more years, as it may not have been an authentic gift!
In High School I attended a number of evangelical and pentecostal youth groups, which really formed the way I read scripture, but did not involve the Charisms. So when I got to the charismatic John Paul II bible school, I started questionings the validity of tongues, but because of my protestant way of thinking I maintained that if they could be clearly defended from scripture, I would consider them legitimate.
To my surprise, there is tons written in scripture about the legitimacy of tongues and the other charismatic gifts! Mark 16:17 Jesus promises the disciples that believers will speak in tongues, Acts 2 (Pentecost) the disciples begin speaking in tongues, In Acts 10:44 where the fact that Gentiles spoke in tongues indicated to Peter that Christianity was not just for the Jews but that the Holy Spirit was being poured out on all, and in Acts 19:6 where the Ephesians had their baptism fulfilled and received the gifts of tongues, possibly foreshadowing the Sacrament of Confirmation.
But to me the most telling passages were the ones in 1 Corinthians 12, 13, and 14. The Bible was not written to a Catechism, or faith textbook, and so in none of the passages mentioned is there an explicit explanation of what is meant by the gifts of tongues, but in 1 Corinthians Paul is countering some of the abuses both in the celebration of the Eucharist and in the praying of tongues, and other things. In doing so and describing what orderly worship should look like, he effectively explains tongues, and notably that it does in fact sound meaningless. Consider 1 Corinthians 14: 2 "For anyone who speaks in a tongue does not speak to people but to God. Indeed, no one understands them; they utter mysteries by the Spirit." or 1 Corinthians 14: 14 which reads "For if I pray in a tongue, my spirit prays, but my mind is unfruitful." Interestingly, brain scans have been done on people praying in tongues, and it was found that activity in the language and control areas of the brain decreased, while those in the emotion centers increased.
Someone reading 1 Corinthians 14 may get the idea that Paul is against tongues, but this would be a misread. He is concerned about abuses of the gift, and even says "I thank God that I speak in tongues more than all of you." but then he adds "But in the church I would rather speak five intelligible words to instruct others than ten thousand words in a tongue." ( 1 Corinthians 14:18-19).
A proper read of 1 Corinthians in context, and then in light of 2 Corinthians, was that Paul was saying that all of the liturgy and charismatic gifts had to be at the service of love, which is above everything else (1 Corinthians 13). Incidentally, this teaching is reinforced by the Catholic Church in the Catechism, paragraph 2003 which says "There are furthermore special graces, also called charisms after the Greek term used by St. Paul and meaning "favor," "gratuitous gift," "benefit." Whatever their character - sometimes it is extraordinary, such as the gift of miracles or of tongues - charisms are oriented toward sanctifying grace and are intended for the common good of the Church. They are at the service of charity which builds up the Church."
This brings me to the next step in my testimony. I eventually realized that though something seems well argued in Scripture to me, inevitably on any issue there will be a range of opinions about what Scripture means. Trinity, Eucharist, Sacraments, nature of Salvation... so on all of these issues, I differ to the authority of the Church. (This is called giving your "assent of faith".) A fun game to play if ever you are wondering what is the correct interpretation on a subject or arguing with someone who accepts the authority of Scripture, is to ask the question "I wonder what the Earliest Christians thought?" If Christians clearly and authoritatively taught something before the Canon of Scripture was finalized (393 AD), well clearly anyone who accepts the canon of scripture ought to accept the authority of the Church who decided on it, therefore they ought to accept the teachings of that Church. Anyway, be it purgatory or trinity or infant baptism or rapture or what have you, the teaching of the Church today is consistent with that of the Church in those early centuries.
So with tongues, what did the Early Church teach? As always, it is perfectly consistent with what the Church today teaches, and that is... that it is inconclusive, undefined. There were some, called Cessationists, who thought that the gift of tongues were for the times of the apostles, and had ceased. These also maintained that other gifts, such as prophecy and miracles, had largely ceased. Among those who seemed to think that were Chrysostom and St Augustine, who described the gifts as being "adapted to the time". 
On the other hand, Augustine also described what he called "Singing with Jubilation" which he described as "Singers... being as it were filled with so great joy, that they cannot express it in words, then turn from actual words, and proceed to sounds of jubilation. The jubilee is a sound signifying that the heart laboureth with that which it cannot utter. And whom beseemeth that jubilation, but the Ineffable God? For He is Ineffable, Whom thou canst not speak; and if thou canst not speak Him, and oughtest not to keep Him silent, what remaineth to thee but jubilation ; that the heart may rejoice without words, and the boundless extent of joy may have no limits of syllables? Sing skilfully unto Him with jubilation."