How deadly is transformer hummm...

I've got an email out to the seller of the amp, to see if he can reach out to Mr. Had, for some advice. The amp was made in April and there shouldn't be any transformer degradation of significance by this time. I would open it up with a little clear-firm guidance, but I am recollecting that my last rash of flirtation, soldering gun in hand, was over thirty years ago in a high school classroom. 

Thanks for the new vocabulary word: isomerics

@wolf_garcia has me interested in the heat resilience of the purchased washers and I've discovered that they are more durable than the skin on my face. According to the Home Depot account for DANCO 1/2 flat washer 3/4" O.D.:

• Can withstand heat between a temperature range of 86°F-248°F (-30°C-120°C)

Would 248F handle the temperatures within the amp @atmasphere ? I'm not convinced, because it's quite hot to the touch, once it been in operation for an hour or more.

Can anyone speak to the expected problems with this kind of symptom? One person claimed it could clear up... I imagine the amp has around 100 hours on it by this time... 

No rubber or BRubber or anything  other than silicone.  I have a few noisy transformers that had mechanical hums. Mounting issues. 

Not all silicones are the same. The super HIGH temp. silicone can be conductive. Silicone washers are OK BUT, read below..

Put your hand on top if it FEELS, mechanical, press down, can you dampen the noise? Turn off, UNPLUG, remove the valves, flip it get a 40 watt bulb with pig tails, discharge the caps. Work.

A little dab will do ya!  LOOSEN the securements. don't remove them.
Get a pin applicator (smaller high pressure needle gun) A small grease gun will work. give it a little shot, not more than a BB amount.  .177-.180
at each securement between the two surfaces. Tighten. Let it dry, and try it.

Still hums

Check the valves, PULL and reseat move them (pencil tap test) around see if the noise changes. BAD VALVE.. Have to check them
Valves are good.

Still hums

Make sure the voltage is 120. I have a few Cary designs, they like 120VAC, not LOW. They will hum. Easy to check and or fix. Voltage maintainer or Variac, will really tell the story. Start at 110v slowly go up, the hum will go away at 118-122VAC

Still hums

????? I'm out of low cost easy fixes, go find a repairman. Everything I offered is under 10.00 silicone an High pressure needle gun.

Happy hunting

Regards

...and now I have email out to Dennis Had...

What you purchased, that I recommended, should be fine with temperature, as the mounting area, does not get as warm as other areas of the transformer. Additionally, heat rises. I would like to see a close up of the transformer mounting area, as I am curious to see what atmasphere is speaking of. I have not run into a transformer that could not be isolated, but obviously, I have not seen them all. I am sure Dennis Had will respond, will treat you with professionalism and respect, and, will look to help you. Maybe he will suggest sending him, or his servicer, the amp.

I believe I found a picture, that allows me to understand what atmasphere was speaking about. The power transformer, seems to be " sunken ", into the chassis, but imo, can still be isolated from the chassis, but likely, not with these that I recommended ( I am sorry ). You can use them on the output transformers, with access through the underside, which is necessary with all transformers, as atmasphere pointed out. I would wait to hear from Mr. Had. I am not surprised you hear the transformer in that thing, close up to the chassis, as it is MASSIVE, for that design. As I said, I hear most power transformers in amplifiers, when close up ( with being careful not to burn myself, as pointed out by wolfie )...lol....I will stay tuned to your progress.