Strangling the sound guy?

As a musician who is also a soundman I must discourage that type of behavior. There could be a myriad of reasons why the system was feeding back that may or may not be related to the soundman being at fault.

The number one cause of system feedback is related to the singer not singing directly into the mic, and or holding the mic improperly. Fact; if you do not sing directly into the mic (this means right ON the mic! no less than a half inch away) than you are losing more than half the volume. (especially with a standard dynamic mic like a Shure sm 58) When this happens the soundman has no recourse but to turn the mic up which often causes it to feedback. This is not the soundmans fault, it is the singers fault for not knowing how to correctly use a microphone. (this applies to anyone singing)

Another big problem is the singer grabbing the ball of the mic and cupping his hand around it. This is a sure fire way to cause very annoying feedback. NEVER grab a mic by the ball! Always hold the mic by the shaft! (yeah I realize how it sounds! this makes it easy to remember!)

A singer who walks around stage a lot is cool, but if they happen to point the mic at the monitors or get too close to the mains (main PA speakers) this can also cause annoying feedback. Once again these are not faults of the soundman but of the singer(s) who are not aware of proper mic technique. The number one cause of feedback is improper mic technique. I always tell "singers" to sing directly into the mic! "If your lips aren't touching the mic, you are not close enough to it!" As I have stated, when a singer backs off from the mic you lose volume exponentially. Once you get to more than an inch away you have lost 80% of your volume level. This is basic mic technique 101. When this happens a soundman will often try to boost the volume of the mic(s) in question but this causes the problem. A mic turned up too loud tends to feedback.

This is a"catch 22" for the soundman. If the singer(s) are not singing properly directly into the mic, no one can hear them and they yell at the soundman to turn it up. This then causes annoying feedback and everyone again blames the soundman The truth is the level was fine but the singer just is not using good mic technique to begin with. Before blaming the soundman ask yourself if your singer(s) were using good mic technique as I have described here? If not, it was not the fault of the soundman, but of the singer(s) The soundman was trying his best to make up for poor mic technique.

If you play in a rock or metal band than this mic technique becomes VERY CRITICAL! This is because rock and metal music is often played at levels that put a PA system to it's limit. By using proper mic technique the soundman does not have to turn the mics up so high that they are picking up all the noise onstage (another prime cause of feedback).

Be sure to do a sound check at the beginning of the event (before the audience shows up) if you are playing in a club that has a regular soundman be sure to listen to his directions, he knows better than you how to get a good sound from the system and from the venue. Be courteous and polite to the sound personnel and to the club employees and do NOT alter your setting after the sound check, unless the engineer (sound man) asks you to. Any problems you are having should be addressed at the sound check. By following some basics and cooperating with the crew you should have a good gig. Your experience is often the one thing that will make or break your sound. Try working with the sound crew and taking suggestions and you should have a good show.

No, I wouldn't strangle him.

I'd kick him out of he booth and set it up myself. I know exactly what he did wrong, and if you know anything about how soundwaves work, you should too.

He had the microphones too close together, and he probably had one or more of them in front of the PA speakers. (causing a loop where the mic was trying to amplify its own output infinitely)

The fact that the mics kept ringing tells me that he didn't fix the overall problem, just fixed the major issue of the howling mic. That guy has no business running a sound board if he doesn't know how to avoid that.