Your concerns are well-founded. While a number of bands are unaware of, or ignore, the clear health-related and halachic ramifications of loud music, it is certainly contrary to Jewish law to have loud music played at simchas (or otherwise). For an in-depth response and much more information on this matter, I would recommend Rabbi Forsythe's article "Dangers of Loud Amplification at Simchas".
Much of the below is taken from (and based on) the above referenced article:
IN LIGHT OF THE CONSENSUS BY ENT’S (EAR, NOSE, AND THROAT DOCTORS) THAT LOUD MUSIC CAUSES PERMANENT AND IRREVERSIBLE DAMAGE TO THE HEARING MANY GEDOLEI HADOR HAVE COME OUT AGAINST LOUD MUSIC. RAV DOVID FEINSTEIN, SHLITA, SAID THAT STRONG EFFORT MUST BE MADE TO PREVAIL ON BAALEI SIMCHA AND MUSICIANS TO STOP LEVELS OF LOUDNESS THAT ARE CAPABLE OF CAUSING DAMAGE. MANY GEDOLIM (INCLUDING Rabbi Yaakov Perlow, the Novominsker Rebbe; four Roshai Yeshiva from Lakewood: Rabbis Malkiel Kotler, Yisroel Tzvi Neuman, Dovid Tzvi Schustal and Yeruchem Olshin as well as the Mashgiach Rabbi Mattisyahu Salamon; Rabbi Shmuel Birnbaum, Mirer Rosh Yeshiva, The Roshai Yeshiva of Philadelphia Rabbis Elya Svei and Shmuel Kaminetsky; Rabbi Aron Moshe Shechter, Rosh Yeshiva Chaim Berlin) SIGNED A LETTER THAT STATES, “THE HOSTS SHOULD INSIST THAT THE MUSIC AMPLIFICATION SHOULD RESPECT THE FACTORS OF GOOD HEALTH AND TASTE, AND NOT DETRACT FROM THE ESSENCE OF A YIDDISHE [SIMCHA].” SIMCHAS ARE MEANT TO CELEBRATE MITZVOS. IT WOULD BE HIGHLY INCONSISTENT TO CELEBRATE MITZVOS BY ALLOWING LOUD MUSIC THAT CAUSES PERMANENT DAMAGE TO THOSE PRESENT. THE SIMCHAS BEIS HA’SHOEIVAH IN THE BEIS HA’MIKDASH DID NOT HAVE LOUD AMPLIFIERS AND PROVOKED SIGNIFICANTLY MORE SIMCHA THAN THE GREAT SIMCHAS WE ARE ZOCHEH TO HAVE TODAY. THOSE WHO DEMONSTRATE - LOVE OF A FELLOW JEW - אהבת ישרא-ל BY RESPECTING THE HEALTH AND HAPPINESS OF THOSE PRESENT WILL UNDOUBTEDLY INCREASE THEIR LEVEL OF SIMCHA.
Furthermore, the following response (posted on "Choshvei Shemo") further addresses the issue of loud music in the context of halacha (Jewish law):
WHAT DOES THE TORAH SAY ABOUT LOUD MUSIC AND OTHER WAYS ONE CAN DAMAGE ANOTHER'S HEARING?
1) In the Talmud, we learn as follows:
"...If he makes him deaf, he pays his (the victims') entire value" (Bava Kamma 85b).
RaSH"I comments on the above that one who causes another deafness has to pay the entire market-value as a deaf person "is not fitting for anything". The Talmud discusses other types of bodily damage, listing the fine of the damager as significantly less than the punishment of one who inflicts deafness upon another. Rabbeinu Yonah says, the person is no longer worth anything when he is lacking his bodily function of hearing. Meaning, hearing is such an essential component in a person's existence that lacking it takes away a significant part of his value (assuming his value on the market, his total value).
2) In Torah law, if one causes injury to oneself (as well as to another), they transgress "bal tashchis d'gufo". "Bal tashchis d'gufo" is the prohibition for one to cause any type of injury or damage to oneself or to another. Examples of transgressing this prohibition is smoking and playing loud music.
3) "Chovel B'Chavero": This is the prohibition of one who "causes damage to another".
4) "V'Ahavta L'Reiacha Kamocha": The Torah commandment to "love your fellow as yourself". One is obligated to act toward another in a way that demonstrates consideration for the other person. When one plays loud music that potentially damages another's hearing, he/she is transgressing the Torah commandment of "love your fellow as yourself".
5) "Chillul HaShem": "Profaning the Name of G-d" - When a Jew transgresses the Torah by misrepresenting the Torah, especially in a way that potentially brings others (both Jew and non-Jew) to look upon them, and, consequently, at the Torah way of life in a disdainful way, they commit the severe sin of "profaning the Name of G-d". When Jewish bands play music at an unhealthily loud volume, they misrepresent the Torah. People may look down upon Torah law for "allowing" such loud music. The Torah actually prohibits such loud music for a number of reasons (at least some of them are mentioned here).
6) Theft (according to the Torah): Aside from stealing by damaging hearing, a band can transgress the Torah prohibition of theft by refusing to lower the volume of their music. If the people who hire the band request the band to lower the volume and they refuse, only to walk out of the simcha (celebration) rather than play less loudly, they are stealing from those who hire them.
