Do you feel you can pop the cover, and while it is powered on, determine if there is a particular area within the amp, the vibration is coming from ? If you can, I believe I can help you. Where are you located ( city ) ? According to the web, the Marantz mm9340 weighs in at under 45 lbs. Dynamat, Peel & Seal ( roofing repair tape ) and others can be used to control resonance and vibration within every chassis. I dampen everything, and believe you me, the sq improves every time.
Cabinet resonance problem with Marantz MM9340 amplifier
The MM9340 amp is a four channel Class D amplifier producing 275W into 8 Ohms and 400W into 4 Ohms. I am using it to drive four subwoofers, which it can drive with ease. The problem is, the cabinet resonates seriously and appears to be in beat with the music. It does not appear to be airborne related nor is it originating from the stand. The resonance appears to generate from within the amp itself. Has anyone experienced a similar problem such as this? Any suggested solutions?