At what vol level do you get rumble / flutter?

Actusreus, you're finally on the right track with the damping fluid. As some have mentioned before, your problem is not an issue of wow, flutter, or rumble. Rumble comes from noise from the motor (usually an old style idler drive turntable) getting picked up by the cartridge. Your problem is most likely a mismatch in cartridge compliance and effective mass of the tonearm, which causes the woofers to visually "pump" at a very low (e.g., 10-13 Hz). Damping fluid can lower the amplitude of the resonant peak. Increasing your tonearm's effective mass can lower the frequency to where it has less audible effect and improves cartridge tracking.

Here is the cartridge/arm compatibility for the Ortofon MC-3 Turbo. Its compliance is 13 and cartridge weighs a very light 4.1 g. The Pro-Ject Xpression tonearm has a low effective mass of 8.7 g. This puts the resonant peak at 12 Hz and close to 13, which is outside the ideal of 10 Hz. If you could add 3-5 g to your arm's effective mass (which you could do with a headshell weight), this would push the resonant frequency down to the 10-11 Hz range which is near ideal. According to the Xpression's specifications, the stock tonearm counterweight can accommodate cartridges weighing from 7-12 g and there's an optional counterweight for lighter cartridges of 4-7 g. As you can see, you have one of the lightest cartridges on the market. Did you switch to the other counterbalance to accommodate it?

Since you're better off sticking with the original counterweight and increasing your tonearm's effective mass to lower the resonant frequency, get a headshell weight, heavy mounting hardware, or both to increase the tonearm effective mass by 3-5 g to compensate for the low weight of the cartridge. This will increase the effective mass to overcome the relatively stiff compliance of your new cartridge. If you do this and top off your damping fluid, the woofer "pumping" should diminish significantly.

You may also want to consider an aftermarket turntable mat to help dampen resonances and further isolate the turntable's mechanical noise from the cartridge. A record grip or clamp may help a bit too; it certainly does on my rig. It doesn't have to be expensive--the acrylic one from Clearaudio or the rubber one from KABUSA.com (both around $30-35) should do fine.

07-04-12: Tobes
Adding mass to the cartridge/tonearm will lower the resonant frequency. Note that warp induced signals are in the 0.5 - 7Hz region, so you don't want to drop the cartridge resonant frequency too low if your cartridge/arm/table already has a problem in this area.

FWIW, I can't recall any cartridges I've used that have fallen outside the broad ideals for cartridge resonance, say 8-14Hz, when a test record is used. However there have been large differences in the amplitude behavior at resonance - no doubt due to the different construction methods of the particular cartridges and arms. ...

Right, but 10-11 Hz is considered more ideal than 13-14 Hz or 5-8 Hz. Adding 4-5 g of effective mass to the OP's rig will lower the resonant frequency from 13-14 Hz to a more ideal 10. However, as you mention, there's the resonant frequency and then there's the amplitude of that frequency. The OP noticed the increased pumping after changing from the stock cartridge on the Xpression (Sumiko Pearl) to the Ortofon, so it seems that there's something in the cartridge swap that increased the pumping. The Pearl weighs 2g more than the Ortofon and is a little more compliant as well at 15 vs. the Ortofon's 13. I don't know enough about the Turbo's housing to form an opinion on its damping, but when you combine a very light arm (8.7 eff mass) with light cartridge (4.1g) and stiffer compliance, you're raising the resonant frequency, and with the lower mass the amplitude would be higher too.

Fortunately the OP's tonearm has a fluid damper, so he may be able to add fluid to lower the amplitude of the resonance. Increasing the effective mass with headshell weights should not only lower both the resonant frequency and amplitude as well.Wrapping the tonearm in PFTE pipe thread tape might help a bit too, both in damping and effective mass. It sure made my Technics tonearm sound better and more linear.

07-06-12: Sbrownnw
@johnny, never had the factory cartridge on my Xpression. Had two mc-3 turbos on it and recently had the ortofon mc 25 fl with the heavier counterweight and it did the same thing (the 25 fl is about 10g). How do I add fluid? Is the tape u mention for my tone arm easily removeable if it does not work out?

Well, it looks like I shot my mouth off without paying closer attention. I realize now that the earlier post about adding damping fluid was contributed by someone else who has a tonearm that uses it. So never mind about that.

Second, one thing that makes this difficult is that what may be a normal amount of pumping for one person may be alarming or excessive to someone else. Third, pumping can come from record warps, how the bass groove was mastered, and tonearm/cart resonance. How bad the speakers pump is relative to the amplitude of the resonance.

If you tape your tonearm, it's reversible. There is no adhesive on the tape; it is very thin and stretchy. However, since you have a carbon fiber tonearm, the effect of an arm wrap is probably minimal. My tonearm is undamped hollow aluminum, so the arm wrap made a significant audible difference. With a more modern carbon fiber arm, probably not so much, but it's only a $1 experiment. We're talking about Teflon pipe thread tape, which should be a buck or two at Walgreen's or Home Depot.

After looking over the entire thread and getting a better feel for your rig, it looks like the KAB RF1 Rumble Filter addresses the various problem sources most directly.

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.