Did it fault while the tech was there, or did he have trouble recreating it? Was the noise a buzz, hiss, whine or hum? Is that sound coming from anywhere specific on the set (speakers, where the power lead gets plugged in, near the antenna or video inputs, etc)? Is it not turning on at all, or is it only running for a couple of minutes before it shuts down?
Without opening the actual case, it's really tough to know what the problem is. If a capacitor in the power supply had blown, the set would probably not even turn on, and ditto if some other p/supply part had failed.
If you had a faulty fan on the power supply (or somewhere else on the set), that could cause a lot of the issues you've seen. However, fan noise is quite easy to hear and diagnose, mainly because a dying fan sounds pretty damn horrible (think grinding noise).
Faulty circuit boards can cause all sorts of errors, but are a ****** to diagnose because of their complexity. Without opening it up on a bench with some testing tools, all you can do is give a complete list of when and how the unit faults to the repairers and let them work from there.
As for firmware, maybe the version he/you put on there didn't transfer properly, and needs doing again. That's pretty unlikely, but it's certainly quicker than sending it away for repair.
Short answer is this, it's not working properly and needs to be fixed. Samsung are the best ones to know what the fault will be, but they'll probably need to get it to one of their service centres to get it looked at.
Here in Australia, you have a certain amount of power to get a warranty repair done even when it's slightly out of warranty, so be pleasant but firm when you speak to them. Samsung's not likely to try to screw you over on the repair, mainly because it's normally easier and cheaper to get it done than to fight over it. Keep in mind that Samsung's warranty people have to think about every single claim on their desks, so be patient with them.
Make sure you keep copies of the unit's serial number and any repair documentation that either Samsung or their repair agent sends you, as this will help them locate it quickly if you need to call for progress. Ditto with any freight documentation, if you need to send it away. It sounds silly to say that you should always know exactly where your screen is, but you wouldn't believe the number of people I deal with every week that don't bother to find out, and then get aggro when it can't be located easily.
Good luck with it, and I hope you have your screen back in full working order soon.
Please help ......I have had this television for 1 year now......Right before the waranty was to run out I started noticing a wierd sound and then the tv would shut off and on again....It did it every once in a while..and I just kept my eye on it...Well It started to do it more often so I called Samsung and had a tech come look at it.....I had already upgraded the firmware myself after reading about it on the internet forums.....The tech came and insisted it was the firmware and the problem would be solved...He installed his firmware which was supposed to be better. Well a couple of weeks go by and bam....The tv shuts down constantly now....What is it..is it a bad power supply a bad circuit board...What??? Can someone enlighten me please. I called again but have not heard back yet. I do not want to get screwed over on this. Help...