Phono cartridge left / right output voltage differ

The difference is ~.1 dB. No, I don't think you can hear that.

This difference is about a .5 db difference. That is well within most cartridge specifications. One can hear a .5 db difference as a subtle shift in the position of the center image in a set up where the center image is narrowly drawn, but, the shift will be hardly an issue (if it is an issue to you, then you MUST have a balance control, preferably one that can be operated by remote control.

The left is .16 mv and the right is .18 mv.

That is great for a Denon.

Well, we have three different statements of what the difference is in db. I would re-assert that it is almost exactly 1.0 db, as I and Mulveling indicated. 20log(0.18/0.16) or 20log(0.16/0.18).

Regards,
-- Al

Just to reiterate - Almarg (plus my own posting) is correct - the difference in your cart is *definitely* 1.0 dB, because:
20 * Log_base_10(16/18) = -1.023

^ You get the same magnitude of result, but with a positive sign, if you flip the numerator and denominator. The multiplying factor here is 20, not 10, because we're dealing with voltage proportions, and power (as eventually driven through your speakers) is proportional to the *square* of the voltage (hence the extra factor of 2).

And that's absolutely quite audible, though I've been surprised by how tolerant some folks (even hi-end folks) are about imbalances up to ~ 1.5dB. It's FAR easier to discern a 1dB difference in L/R channel level than it is to notice a 1dB change in level for both channels. In my system, center image would seem shifted by about a foot. I've found myself annoyed by imbalances down to 0.5dB or even less (an almost certainty with vinyl).