tone arm drifts towards the outside when lowering

I'm setting up a new table and cart. set the alignment, VTF, VTA and it sounds very nice.

When I lower or raise the tone arm it "drifts" to the outside.

It tracks fine on the record.

Does the tonearm have an anti-skating adjustment? If so, check to make sure that it is set correctly (i.e. too much anti-skating force will cause the arm to drift to the outside when lifted).
Is your turntable level?
Also be sure that the turntable is absolutely level.
correct directives from the previous 2 posters. Use a bubble level to make sure the table is level. Also, make sure the arm is perpedicular to the table itself. If you have an anti-skating adjustment it could be set very loose in the sense of it trying to counteract the rotational forces exhibited by the TT. You want the anti-skating force exerted on the arm to be pushing towards the center of the platter. Also, check your down force adjustment to make sure that the cartridge is sitting on the surface with not too little pressure. Now, here is something that effected my setup in the same way. I had rewired my tonearm and after seeing the same phenomenon as you, I realized that the wires were oriented in a way as to exert some force on the tonearm. The tonearm would just lightly move as you described until I re-adjusted the positioning of the wires in relation to the arm mechanism. Good luck.
An issue here. Quoting VPI , without anti-skating , and using a pivoted arm with an offset head, "Putting a stylus down on a flat grooveless record will cause the arm to shoot in toward the center of the record." If you use anti-skating at all (some don't), you want to COUNTERACT this tendency, not bolster it. Thus the OP's situation is better than the opposite, but it sounds like he has a bit too much anti-skating, for whatever reason.
check to make sure the contact points between the arm and lift platform are free of dust and oil.
Check your antiskating by carefully viewing the cartridge head-on while a record is being played. Viewed from that perspective, the cantilever should be at the same left vs. right angle relative to the cartridge body that it is at when the stylus is lifted off of the record (which for most properly designed and manufactured cartridges will be straight ahead).

In my experience, most of the guidelines for setting anti-skating force which may be offered by tonearm or turntable manufacturers result in too much force being applied, and I have typically found that about 2/3 of the recommended setting gives the right results.

-- Al
Assuming a tonearm is unconstrained in the lateral plain during cueing (everything level, dust- and dirt-free, low friction bearings in good shape and properly adjusted, tonearm wire twist and other lateral forces eliminated, little friction between armtube and cueing support), then any amount of anti-skating applied during cueing will move the arm outward. That's what anti-skating devices do, push or pull the arm outward.

Actual behavior varies from one arm design to another. For example, outward cueing drift is typical with Rega arms and their clones, because (1) the anti-skate device applies some force even if set to "zero" and (2) that force is always on. OTOH, cueing drift on a TriPlanar is avoidable. Aside from the option of making anti-skate truly "zero", the anti-skate device is readily adjusted so that outward force is not applied until the stylus touches down.

Other designs may vary in other ways. Check all the factors posted above. If all seems okay then investigate the anti-skating functioning of your arm. Its design may or may not allow you to mitigate outward cueing drift.
thanks everyone.

I removed the anti skate and the problem went away. not sure if I can hear a difference or any issues with tracking.

table is level and I triple checked the VTF -- all good.

will try cleaning the lift

the table is the pro-ject RM 10 with a shelter 901 cart.
Interesting that I have just, in the last month, begun to notice this behavior in my arm: an RB700 mounted on a Basis 2200 Sig. Both arrived new in May of this year and as I say, the drift is a recent development. It was set up for me by my local tech (who I trust implicitly, he's not new to this). I will check my table for level asap.

As dougdeacon points out perhaps this is just a feature of the Rega arm. But if that's the case, would it not have been that way from the outset?

FWIW, cart is a Dyna XV-1s.
On second thought, maybe not. I do *use* the arm :-)

But if there are any other thoughts/opinions, fire away!
Problem resolved --

I cleaned the lift -- it was dusty/dirty.

My mistake on the set up -- I had the anti skate set up prior to adjusting the VTF.

Those two simple changes did the trick.

Thanks again everyone.