At what vol level do you get rumble / flutter?

I forgot to mention my turntable is on a custom steel wall rack bolted to the studs in my house but is in an audio cabinet (no doors). The section of the audio cabinet that houses the turntable has some of the back panel removed so the steel rack arms can come through. Could my problem be caused by this setup?

BTW, I put a new Vincent Pho-8 up against a new Pro-ject phono tube box II (my demo one was replaced under factory warranty after 1 channel got noisy) this weekend. The Pro-ject won out with better sound stage, realistic instrument sound and just overall more musical. I hope to upgrade the wall wart for the Pro-ject tube box. Would this one be a higher quality less noisy power supply?:

http://www.powerstream.com/EA1050.htm
EA1050A-61 16V 4A 5.5x2.5x11mm $57.50

Thanks everyone,

Scott

I added a pict of my entire system (on my system page) to show the config. Turntable is in the upper right corner.

07-18-12: Sbrownnw
@johnny, my table is at my dealer now. It has the lighter 65g counterweight for cartridges between 4-7 grams. How do I calculate the effective tonearm mass with this lighter counterweight (10g lighter that the factory 75g for 7-12g cartridges). I might have him put in a pair of 1 gram brass screws to bring the weight up a little.

The change in counterweight doesn't change the effective mass of the tonearm. Effective mass is only the weight of the tonearm from the pivot point forward to the headshell. Once the cartridge is mounted, total effective mass includes the effective mass of the tonearm plus the headshell if removable, the cartridge, and mounting hardware. Standard mounting hardware is about 1/2 gram. Since cartridges have a wide range of weights, you use a heavier counterweight to balance a heavier cartridge. The heavier cartridge increases effective mass; the heavier counterweight does not; it simply enables you to get the desired tracking force from a heavier cartridge.

Point of order. Effective mass of the tonearm is really the moment of inertia of the tonearm. The moment of inertia is calculated using I=mr^2. That means if you switch the mass of the counterweight and do not move it then the moment of inertia will change proportionally. If you must move the counterweight in or out, the moment of inertia is going to change by the square of the distance.
The angular momentum is I times rotational speed or like mv in linear terms. Angular momentum affects how quickly the tonearm moves or reacts to force changes. The force changes come from the stylus to record and through the suspension system of the cartridge
That means the natural frequency of the tonearm cartridge system is dependent upon its inertia, or effective mass divided by the spring rate of the cartridge and then the square root of that.
Long story short, change in counterweight mass as well as moving the counterweight in or out will change the Fn of the system. A lighter cartridge reduces mass and also allows you to move the counterweight in. So effective mass of the tonearm/cartridte goes down. If the spring rate of the lighter cartridge is lower (higher compliance) then the overall system natural frequency may remain nearly the same.

Hi Sbrownnw,I haven't compared specs, but this is a very popular regulated switching power supply.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-532

Not all records have built-in rumble, and even a cu/arm mass mismatch, tends to be dwarfed by acoustic and mechanical feedback, causing pumping. Spikes mass couple to the mount. Perhaps if you decouple your table from the shelf, it will help. That is another shelf under the table and supported by inverted cones. If you've already done this, sorry I missed it.
Regards,