Cabinet resonance problem with Marantz MM9340 amplifier

Although I am on a dedicated circuit, I own a particular Hafler designed amp ( Smart Theater Systems TA 242 I acquired from a going out of business movie theater ) that uses a toroidal transformer. When connected through my system, the transformer " hums " when I am using my OTR microwave. From the chassis only, not through the speakers. Yes, I damped this chassis and isolated the transformer using a few layers of Peel and Seal, and the hum is much lower, but I can still hear it. I suppose I can stop the humming by teaching it the words.......not my joke....Enjoy !

@mrdecibel That hum is caused by a DC offset in the power line.   It happens and only a volt or three will cause it.   There are several devices made to eliminate this, as the problem is worse with toroidal transformers.  If you Google "Blocking Mains DC Offset From Transformers", you should find lots of stuff to fix that.   There is a good article here: https://sound-au.com/articles/xfmr-dc.htm

If you scroll down a bit on that article, you will find a schematic so you can home brew it.   I did cost it out and found you can buy ready made DC Blockers for about the home brew price, assuming you bought parts from DigiKey or Newark Electronics. 

Which, BTW, reminds me I should try a DC Blocker to fix my problem!

Some article. TY. I guess it would not harm anything by investing in one. 

There are a lot of options out there.  iFi makes one, although a bit tiny.  I bought this one from these guys - https://www.atlhifi.com/product-category/fully-assembled-devices/

If you do buy from them, I suggest you don't use US Mail, as it takes forever to arrive.   It is well made, rugged, and clearly will do the job.

There are other options from other manufacturers, too.   You are right, it won't hurt that is for sure.  

A final follow up on this resonance problem.  I covered the inside of the unit with DynaMat Extreme.  Turns out, it helped significantly!  I put two layers under the transformer and that seemed to help as well.   It reduced the resonance a bit but more importantly, it cleaned up the entire bass region.  The bass has much more "impact", you can feel it "hit" which before was just more of a muddled mess. I told my wife the bass now had a "visceral impact", to which she agreed  I also noticed that switching from an 18g generic power cord to a home brew 10g shielded cord made a very slight improvement in the muddiness as well.   

Thinking I am on a roll here with isolating the transformer, I added four more layers of DynaMat Extreme under the transformer, which required changing to a 5/16", 5 inch long bolt to secure it.  That is one inch longer than the factory bolt.   It should not matter with a toroidal transformer but I picked up a non magnetic stainless steel bolt and hardware.   I also added a bit more DynaMat Extreme in a few places that still had bare metal.  I could not add any to the bottom of the chassis since there wasn't room for it and the PCBAs.  I thought about putting on the outside bottom of the chassis but I didn't want to mess around with the DynaMat Extreme on the outside of the unit.   The improvement wasn't as dramatic this time as before, but the improvement is now to the point where I can happily live with the result.   The fact is, probably 90% of what I play has bass but not in the extreme bottom end that aggravates the resonance.  

It was then I remembered I had a Panega AC9 power cord I bought just for this amplifier, but removed it when I rearranged equipment in the rack.   So I installed that and it made a slight improvement over the generic 18g cable.  To be fair, the improvement was only in the deep, subterrain bass region.   The bass and upper bass wasn't affected as much as I could determine.   

Thanks to all who contributed ideas to my problem here!