New motor for Nottingham Interspace

Before giving up on that motor, which should last a very long time, I'd check a few things, for starters. Not certain of what kind of noise you refer to, but here are some possibilities. Make sure that the groove in the motor pulley and the platter are aligned. Otherwise, the belt can pull the motor shaft out of its perpendicular (to the platter) rotation and induce noise. Also, make certain that both the groove and the belt are free from crud. A small bit of debris sticking to the inside of the belt may click as it passes the pulley and resulting in a thumping noise. Lastly, and perhaps most importantly, make sure that the pulley shaft is perpendicular in the motor housing as it sits at rest and when in use. There is a grub screw to hold it in place and, if it is loose, the shaft can get out of plumb when the belt is stretched to fit around the wheel and platter, thus inducing noise.
Of course, anyone could get a bad motor, but those 'Not motors are rugged and will last many a year. Doubt yours is feeling ill yet.

Well, I suppose there is always some benefit in taking AC out of many equations. Whether you will notice a difference between the Interspace motor and a DC motor or if any such difference would be discernible, thereby justifying the cost, is debatable, IMHO.

The motor should be dead slient when played, though it will very lightly humm at idle (as desgined). If you can hear it when it spins, other than some very faint belt noise, check all your angles again. If still noisy, I'd suspect a faulty motor and Not will remedy this for you - depending on age, etc.