Make sure there is nothing on the magnet part of the platter. Also, sometimes, the screws that hold down the plastic protective cover underneath the platter might not be seated all the way. Lastly, look at the bottom of the magnet, and make sure that it is in tact, and nothing is bent, broken, or cracked.
Other than that, try switching out the platters from your other turntable, and see if the problem persists. You need to rule out what it is not, before you can proceed with finding out what is the problem. So if the noise moves to the other turntable, you know the issue is with the platter. If the noise remains on the same turntable, then you can rule out the platter being the culprit, and can isolate the issue to the turntable. I've never heard of this, and I've fixed well over 3000 Technics 1200MK2/MK3/MK5 turntables in the past 10 years. I am also considered THE 1200s MASTER. So, I am not sure what could be causing this noise, other than some foreign matter. If your in the NY metro area, bring it on by, and I'll take a look at it, or give us a call, and I'll try and refer someone locally for you: