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You have a RG so it's not a spoke issue. You said it started after new tires, this could only happen from two most likely causes. One, you have one or possibly even two defective tires. You may have cord separation, maybe an old tire sitting around for a long time, etc. The other cause is tread pattern, this is comon in some tires as they are designed with grooves along the circumference of the tire. In it of itself the tread issue is not dangerous but it could be unnerving. The only other problem would be installation of the wheel after the replacement, loose bolts etc. This is unlikely but possible. It's also very unlikely it's a balance issue, this would give you a vibration or tire hop at high speeds and not a drifting feeling. I would take it back to the installer and complain.
are they a matched set? were they mounted with the tires going in the correct rotation? Who did it? Are the wheel spacers back on correctly have you checked rear wheel alignment
If you have D402s or Michelin Commanders, you will think your bike has turned into a professional dancer across grated bridges, rain grooves and grooved pavement. Try E3s or Metzlers and your problem will likely be resolved.
+1 - My first 2 sets of OEM Dunlops were squirrely on metal grating. Switching to Metzler 880's with diagonal grooves solved the issue.
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