How can I reduce RF interference from LED light tubes?
You bought LED replacement "tubes" which are called plug-n-play and allow you to not mess with the ballast -- but also require you retain the ballast.  You are now married to the worst of both worlds: the EMI/RFI output of the legacy ballast, which could be considerable for a magnetic ballast, and also whatever EMI is coming from the new LED "tubes", which can also be considerable if they're cheap. 

If you really want to go LED, you would be better off going with LED direct-wire replacement "tubes", and bypassing the ballast.   You may want to consult the Sylvania documentation and see if they are capable of also operating in direct-wire mode; some are dual-mode like that. Don't just give it a whirl.

Otherwise pull down your fixtures, see how they are wired (instant vs rapid start, 1 vs 2 wires per lamp end) and get direct-wire LED "tubes" which are compatible with your lamp wiring.  And bypass the ballast.  Be sure to consult the factory to learn what kind of EMI the LED "tubes" will be emitting if any.   

Plan "B" is to find a quality ballast with known very low EMI, and change that ballast, then either try your LED "tubes" or just use real fluorescent tubes.  The light from them is superb these days, better than LED. 

Plan "C" is that they make DC power supplies with the same formfactor as fluorescent ballasts.  I scored several hundred of them on eBay for nothin'.  Then get LED strips, two 5m rolls of 3528s should replace 3 fluorescent tubes, and cut them to fit in the fixture and power them off that DC supply.  Obviously, the EMI output of the power supply will be the ruling factor; DC LED strips have no EMI at all unless you dim them.

Lastly, check your grounding.  If your grounding is less than tip-top, it will greatly increase EMI.  If the grounding is not tip-top, make it so, remembering that Code now broadly allows retrofitting of just a ground wire.